If it's streaming numbers, then I'd imagine it means more younger people since older people are probably more likely to watch on cable. Also interesting is that ESPN Sunday Night Baseball is up significantly from last season as well, in all the key demographics (so it's not just old people).
Pandemic ratings were down for every sport, so it's possible this is just a correction to the mean, but the streaming numbers are definitely a sign that more people are interested in watching baseball. I have no idea what that is attributed to, but one thing that MLB has greatly improved on is their footage going viral. When something happens in a game, it's instantly on Twitter now. Previously MLB was very protective of their footage so it was harder to find baseball content on any social media platforms, but I'm guessing someone in the sport smartened up and realized that they can use Twitter, YouTube, etc, to their advantage. They are likely reaching more people now and maybe that has helped create more interest in the sport.
If more people are watching Three True Outcomes baseball, then that's a good sign for once they start implementing some rule changes to create more action.