I agree. I really wanted to believe that this wasn't suspicious - because imagine that if it isn't, it's a pretty hefty accusation to lever at someone. Also, my son is super inept at talking to girls....what if this guy was interested but bad at reading body language and taking hints, and just left when he knew there wasn't a connection?
However, IMO - even if no one at the food truck was involved, the girls were moving away from him, they turned their back to isolate away from him as he seemed to try to follow their movements without any reason for being at the truck - he arrived at the same time, did not seem to be with anyone else and did not purchase from the food truck. He left once he saw them gone. Doesn't mean he left and just didn't go home.
My head thoughts - how long would it take to walk from the food truck to the house? Whether this dude or the other guys they were talking to...or someone not even mentioned? The girls Ubered - but if someone knew where they lived, could that person walk it in the hour or so before the murders took place?
I am sure that whether it was the food truck, the bars, the party, or wherever, that police are tracing driving and walking paths from those to the house, and finding any footage that would show anyone headed in that direction at that time of night.