The Shulchan Aruch[1] rules that single men who do not live with their families must light Shabbat candles in their rooms. The Mishna Berura[2] adds that this is so even if they eat elsewhere. (This topic is subject to a separate discussion.) Regarding your question, the Mishna Berura[3] says that the candles should last long enough for the individual to use them when he returns; otherwise, his beracha is l’vatala (in vain). This seems to be based on the Shulchan Aruch’s[4] ruling that if one lights in her house but eats in her courtyard and the candles will not burn sufficiently long for her to use them, her beracha is l’vatala. What many women who go out for the meal do when they are not confident that the candles will be lit when they return is to have some benefit from the candles during twilight.[5] This works because women accept Shabbat upon themselves upon lighting. Presumably, however, your guest does not accept Shabbat with his lighting, which is common and the correct thing to do if he did not previously daven Mincha,[6] and therefore he could not use this system. Consequently, at first glance, what your guest did was necessary to avoid the problem of beracha l’vatala.
However, the sources above discuss situations in which one had no intention to use the lights. The rulings of the Shulchan Aruch and Mishna Berura cited above do not apply here, because in their cases, there is no difference between what the lighter planned and what occurred. Given that your guest’s regular practice is to benefit from the candles after he has accepted Shabbat, and something arose to alter that on the Shabbat in question, could he have fulfilled the mitzva based on his intention, even without having returned? The answer depends on which of the following formulations of the mitzva of lighting candles is correct: 1) The act of lighting candles is a matter of k’vod Shabbat, i.e., honoring Shabbat by making preparations on Friday to make it pleasant; 2) One must ensure that the house he occupies is set for pleasant usage on Shabbat; 3) The mitzva is oneg Shabbat, one’s personal enjoyment of the light itself on Shabbat (parallel to eating tasty food), but on technical grounds, this must be prepared before Shabbat.
According to #1, your guest’s visit at home was unnecessary. At the time of the lighting, there was an expectation that the light would be of value. Therefore, at that time he honored Shabbat, and this is not uprooted retroactively by changes in the situation. (If one often does not benefit from the candles, then his “plan” is disingenuous and his lighting is valueless.) The same is true according to #2. His room was properly lit, and it does not matter that he unexpectedly was not there at the relevant time. According to #3, however, your guest’s actions were necessary, because if he did not actually benefit from the lights, it turns out that the mitzva was not fulfilled.
One can find a basis for all the formulations, but in this forum we can only scratch the surface. The simple reading of Rashi[7] is that the mitzva is kavod (#1), whereas the simple reading of Tosafot[8] is that it is oneg (#3). The Rambam[9] mentions kavod and oneg, but his language implies that #2 is more to the point. Possibly, whereas the mitzva was instituted with the expectation that people will benefit from a peaceful atmosphere (shalom bayit),[10] the formal mitzva and its beracha relate to the act of kavod, which is accomplished by lighting candles.[11] This idea is bolstered (but not proven) by the facts that the beracha is recited well before the main benefit[12] and that if the candle was lit too early, it has to be relit even if it could have remained burning well into the night anyway.[13] (One telling matter is the machloket between the Magen Avraham[14] and R. Akiva Eiger[15] regarding whether one can make a beracha if she needs a non-Jew to do the lighting for her. Although the act is performed by someone to whom the mitzva does not apply, the result is the same.[16]) However, it is difficult to deduce particulars conclusively from the general concepts that can be applied to every specific and somewhat uncommon situation, especially when it is not always clear to what extent the concepts are mutually exclusive or complementary.[17]
Since the simple readings of some of the poskim require your guest to return and it is difficult to prove them wrong, you can applaud his diligence, all the more so if he acted in a way that did not negatively impact others. On the other hand, we would not label failure to do so a breach of halachic responsibility.