In my experience, there are a significant portion of "foreign nationals" who work in the US that are supported by outside teams. I've worked with folks who admitted to hiring "consultants" to write their code, write their presentation, etc... So they always look so much better than the next guy, get promoted, and seemingly perform miracles.
Chances are this guy has dozens of low-level engineers, maybe PhDs working for him from other countries. He sent them code bases, specs, or anything else so they can do his work for him. They had better trace this and figure out how deep the rabbit hole goes. Also find out who of his "friends" are in on the act.