In which circumstances is the identity of a miner known?
No, it's not necessary to disclose the identity. As Pieter commented below, "foundBy is a feature of blockchain.info, a privately operated website, which gives a guess about the creator of a block. It is by no means something that's part of the protocol". 

If you look at the receiving address of the block's coinbase, you'll see that BitFury sends all their block rewards to that address, so that's probably how blockchain.info arrived at their conclusion.