Backe mentioned "all five" trialists - you listed six there. Can't imagine they would waste an international slot on Alvarez (I assume he doesn't have a green card).
Good question. The guy was playing for an NPSL team and he's 18. I assume he has a green card because I can't envision an NPSL team getting a P1 visa for one of their guys. Maybe he had a student visa? Anything is possible.