How did they know the charger was there in the first place? How far did they have to go to get to that charger? It's unusual behaviour and it should be reported to security.
This would be my concern. It was obviously not the first time he had done this by his actions but how exactly did he know the charger was there without wandering in and out of places he shouldn't have been and rooting around in the first place?
Exactly. I think that the OP identified the man as a cafeteria worker to indicate that he was in an area of the building far from where he had duties. I think that this business needs to put locks on office/conference rooms. I would have felt very strange to be in an isolated area with an unknown man.
If the offices were closed, it seems like the cafeteria would be closed, too. If the man were on a search for unreturned dishes, it seems like he would have had a cart or tote of some kind to put them on because they would be grungy. The OP didn't mention hearing a cart or seeing a tote of any kind. The whole thing seems very odd, and security should be notified.
OP, chances are that this guy is just clueless. However, I don't think that you should be by yourself there after hours. If he is some sort of a villain, you don't want him to get the idea that he could come after you.
This may sound a bit extreme, but my husband is retired from law enforcement and I have heard the tales of things that were done.