Strava has to be one of the biggest opsec failures in recent years.

Good pace at least

So... He must have been using shipboard wifi. I can't imagine they're allowing private satellite internet solutions, and phone signals aren't going to cover very far from shore.

Why would they not block things like Strava at the network level?

This isn't just an OpSec failure by the sailor, but from whatever team handles shipboard communications as a whole.