It's because Alphas when aroused doesn't leak fluid from thier ass's this is an Omega's thing, and for now he doesn't know yet that Aerock has become an Omega he thinks he is fucking an Alpha.
Ho could connect the dots tho.. nice scent, sweet tears, nice lubrication and the imprint. He's clearly just dumb lol
I don't know if this will be shown in the manhwa but in the novel he will connect the dots (the things you mentioned) and he will find evidence but still couldn't believe it until he hear it from Aerocc himself because the man when he first met Aerocc, Aerocc was an Alpha emitting Alpha sent.
In the novel Aerocc told Klopp that he changed into an omega just recently after he met him.
You're really bad at explaining.
He's so stupid he can't distinguish between arousal fluid and cum..