I’ve blocked ads for so long that I don’t recognize the logo in the corner anymore, but that’s the ad provider for the app you’re using. It probably has a profile of you based on what’s going on around every place their ads are shown and on other trackery things. So not just your activity in one app.

Advertising seems to be against the spirit of Lemmy in general, I’d be upset even if the ad wasn’t this gross. I’m using Voyager and I’ve never seen an ad.