hmmm....idk....it only has four total tailihgts but the steering wheel is the same color as the rest of the entior and has the impala symbol...anything else i can look for?

Of course... it'* been a year and a half since the last time I've even driven a Bonneville. :o

The tail lights are the biggest distinguishing feature, and the most certain. Unless he replaced the trim and lights with Biscayne stuff, which would be to no point, as the Impala pieces are cheaply avilable from JCWhitney and other places. The side trim is different, but I can't recall what the differences were.
Probably a quarter of the Impalas doing the show circuits and bumping down Main St, are actually rebadged Biscaynes with the extra tail lights added on. Kind of like the Tempest/LeMans GTO clones.
Don't let it stop you from getting the car, though. If you want to, you could leave it as is, or complete the Impala conversion with the appropriate tails, or change it back to a complete, original Biscayne.