I'm not on the Tapastry team but I was watching it develop for a while on the sidelines. I'll try to clarify from my understanding.
The Tapas community is everyone who posts a comic or on their own. Until now we didn't have collective name that we liked for this community. Now we do.
So now we can focus exclusively on Community events that are separate from Tapas-wide events. Hence the Tapastry specific social media.
This is only the first step of many this year in Tapas's plans for rolling out a lot of stuff for community creators.
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A community series is anything that an individual user creates and posts that isn't in official partnership with Tapas. So no this isn't about more exposure for Premium titles, but rather home-grown content.
Hope this helps rather than confuses further xD