You shall become my friend, please don't resist.
VS
He clearly has to be racist or have ulterior motives to try and be friends with me.
How often in fiction does the latter ever win anyway?
In his defense, it seems like the backstory of 99% of non-humans in these isekai is that they've already been put into slavery, are being approached by seemingly nice people only to be put into slavery, or to be framed for a crime. So being approached by anyone is suspicious.
And in this case he was approached while being actively discriminated against, so he was already primed to be on the lookout for that.
And even if the character knew that he was being approached by the protagonist... That doesn't seem to always be a safe bet either. So many protagonists are on a power trip, or have massive scary secrets. In this case he's literally being approached by a 300+ year old Dragon Demon General that has spent 300 years getting brainwashed by ancient monsters into thinking they were good guys and that the hero is bad. So he is very very very right to be suspicious.