I mean no, I don't think accidental grooming is a thing, even then he's not shown doing anything inappropriate
noo TT it's a one sided crush by a kid how is the adult grooming him
No, it is not grooming. Grooming is when an adult purposefully targets a minor by establishing an emotional connection with them to make them more likely to agree to sexual advances or less likely to recognize sexual assault as what it is: assault. As Tanaka was unaware of his one-sided crush (one-sided is VERY important here as well since Tanaka did not like him romantically or sexually), he could not have groomed him.
w/ tropes like this popular lately, does this count as grooming when the older one is pretty clueless about the younger one's childhood crush? (also, tanaka reminds me of a certain ml, like kim dokja maybe or subaru)