This is normal and expected. Finding a block is based on probability so it's natural to have two pools mine competing chain tips. The network goes along with whichever chain has the most proof of work.

If you're a miner and you see the network has already accepted another block it's best for you to start mining on top of that one and move on.

Alternatively, in this example, Foundry could've kept mining on their found block and hope they get the next block before Antpool gets theirs. This is risky though because if they don't then they're falling behind and wasting time and energy. Unless they're desperately trying to undo a transaction it's more economical to just move on.