http://www.sptimes.com/2002/01/10/TampaBay/Pilot_s_parents_had_t.shtml Yep, his GREAT-Grandfather was the one that emigrated from Syria in the early part of this century. And again, there basically was no Muslim immigration to the US at that time; it was almost universally Christian.
His GRANDFATHER, Robert Bishara, is the one that doesn't speak any Arabic (but one would presume his father, Charles Bishara, also doesn't either.)
A teenager writing a suicide note that praises Bin Laden doesn't make him a Muslim.
It sounds like someone inspired to get attention with his suicide; prior to 9/11, he likely would have committed suicide in a more mundane way with a more mundane note(parents, interestingly, both attempted suicide at a young age. Father was a small-time hood.)
I think he was mentally ill. I don't discount a drug reaction too.