Well, there isn't really a way around automated filtering. Spammers and malicious actors also send their stuff in bulk. And those big tech companies already have human content moderators. Usually in some poorer countries and it's a horrible job. I suppose there just arent enough humans to also deal with the flood of spam, manually.

These systems are far from perfect. And I'm not really an expert. I don't use Meta's platforms. I can't tell much from that screenshot. It's missing the URL and it hints at some rule that might be shown below.

And I didn't want to say "trust Meta". Quite the opposite. I just think this one specific claim could be true. Not everything is a conspiracy theory. We know they have automated apamfilters. And we know these make a lot of mistakes. Very similar with what other spamfilters do with short URLs. I'd say the simplest explanation is: their spamfilter sucks. Not that they somehow conspired, wrote additional software to deliberately target Pixelfed instances, but just when it's a short post... No. I think in this instance it's the simple explanation.