He blocked you because other people don't communicate directly, and it's safest to interpret decisions like your declined add as a desire for distance.

Unfortunately, it's essentially normalized in OLD for people to never actually say they aren't into you, or to say when they don't want to talk.

People signal disinterest or discomfort in really weird and unclear ways.

"Something came up" sometimes means "I'm busy" and sometimes it means "I don't like you."

Same goes for silence. Or slow responses. One-word and brief responses. Or the classic "Let's be friends", which can mean either they literally want to be friends, or they don't want anything to do with you.

Male-bodied people have to interpret any possible sign of disinterest as literal disinterest to avoid accidentally stepping over unstated boundaries, at worst, or wasting their time, at best.

Honestly? His decision was hasty, but not unreasonable. Someone declining to connect via social media is something most self-respecting AMABs would interpret as a sign to back off.

As someone who relies heavily on explicit and clear communication, I wish I'd adopted his mentality a lot sooner, tbh.

People want to connect, or they don't. Your boundary was perfectly reasonable, but you didn't add him because you didn't like how he approached interactions with you. He correctly interpreted your unstated discomfort, and decided to disengage.

You didn't offer him a way to change his behavior. He has no way of knowing why you wanted that, only that he's recieved a sign to back off. So he did.