There can be vast differences in reading comprehension and contextual tone recognition.

As an easy example think of the many degrees of neurodivergency.

Secondly, British sarcasm and indeed a lot of British communication in general comes from the intention to be deliberately vague, so as to bake plausible deniability in to the responses given.

It can be inferred, but it's not a guarantee.

That being said this guy seems to just be a prick trying to walk back something that blew up in his face.

If you want to act like a dumbass even ironically, you don't get to be mad at people treating you like a dumbass

I'm quite familiar. And in plain text it's often lost on those that would benefit from understanding it. In some contexts it doesn't matter. In others it does. Sometimes clarity is more important than whether or not it falls flat.

You don’t need tone for sarcasm, because it can be inferred from context. Check out British (“dry”) sarcasm.

you're being sarcastic here, right? /s