While this may be great for him, this is probably counter-productive for the org -- and he's preparing to be left out of a lot of decisions and conversation.

I've been in an org where there were stragglers who didn't want to use Slack for whatever reason -- "I'm too old" for it was one I found particularly retarded.

Communication is key -- get your whole team on one tool - silence notifications if you have to, but you should aim to participate.