I can't see the other chain? Been using a BIP110 Block Explorer out of curiousity, but block you mention is also mentioned as having been mind by AntPool.

What is the significance of this?

Some people celebrate the miners controling bitcoin. Maybe today they did something you agree with. tomorrow they freeze non KYC coins, the next day increase block reward and remove 21M cap. They already talk about this. We need Bip111