My guess is that there’s a bot (or very bored person) monitoring a few major communities and they just DM everybody who posts there. I took a bit of a break from social media a while ago and the first time I commented after that, two fediverse chick DMs. Seems like they are responding to activity.
“Better” doesn’t always mean “smaller”, especially in this example. LZMA’s strength is that it compresses very small but its weakness is that it’s extremely CPU-intensive to decompress. Switching to ZSTD will actually result in larger downloads, but the massively reduced CPU load of decompressing ZSTD will mean it’s faster for most users. Instead of just counting the time it takes for the data to transfer, this is factoring in download time + decompression time. Even though ZSTD is somewhat less efficient in terms of compression ratio, it’s far more efficient computationally.
How did you get my nudes?