Okay: (1) he shouldn't have been in this country, (2) he shouldn't have been going to high-school here (though some high-school seniors are 18, so "18-year old adult" is a bit odd in this context), (3) he may have committed sexual assault, rape (either forcible or statutory), or other crimes with high-school girls as victims, and (4) if there are multiple counts against him the characterization as a "predatory" may well be spot on.
However, an 18-year old male taking a sexual interest in high-school girls is not pedophilia, whatever the state's age-of-consent laws may say. In fact it is normal. Heck, if the girl is 16 or older, it doesn't even violate the standard half-plus-seven-years rule of non-creepiness.