I figure Deku would be happy to talk strategy using his notes on Sero’s ability, and Sero’s just the kinda guy who casually holds people while they’re talking. Because, you know. That fella got arms for days. And Deku really needs more hugs.
For some reason I headcanon that Sero is the oldest brother from a large family which is why he acts like such a class dad all the time, but as a result he misses casual physical contact from playing with/hugging his siblings and makes up for it both consciously and unconsciously with his classmates in 1A (got to avoid that touch starvation somehow).