No, this is false as far as I can tell. I am willing to be corrected by someone more knowledgeable but my understanding is:

Communities are implemented not as hashtags, but as special users who “boost” everything addressed to them. That is why Lemmy sometimes gets posts made on Mastodon that mention a Lemmy community. It doesn’t always look great: discuss.tchncs.de/post/45785836

So communities and hashtags aren’t the same thing. In particular, communities have moderators who can remove things or ban people. Hashtags don’t.

It is a feature of Lemmy that all new posts (not, AFAIK, comments) also get the community name added as a hashtag. This is what OP was seeing and serves to somewhat increase the reach of Lemmy posts. But you can’t follow microblog hashtags on Lemmy.