How did this block end up on blockchain.info?
Blockchain.info is a special Bitcoin node created especially for it's purpose. So, it will act differently as well.

I suppose Blockchain.info's created configured it so to keep a record of all information it comes across, including orphaned blocks.

You might think that it is risky to do so because knowing this, people can try to flood the servers with irrelevant data. However, even with difficulty 1, it costs way more resources to create valid blocks than it will take for Blockchain.info to store them. It will only be possible to add a block every few minutes with regular mining hardware. Considering the mining profits you could earn by regular mining, I think it's safe to suppose no one is going to try flooding the Blockchain.info server.