When a shiny, boss, or whatever else is announced when there are at least 2 players online, it almost always says the wrong player is near the spawn. I've had it before where I'm in a snowy biome, with no other biomes within 1000 blocks, and it says that something spawned in a flower fields near me. In reality, it spawned next to someone else nowhere near me, in the biome specified. I'm not really sure how to 'prove' this, as I can't think of how to make screenshots include all the necessary information, but I'm very happy to provide anything that'd be useful.