How did this block end up on blockchain.info? How did this happen?

https://blockchain.info/block/000000004b7959f66c9dab42b8933f0a43c9705bd9bd486de3a69407fb072cd3

That's a fork of the original blockchain (started from genesis block) which was 9 blocks long and appeared in 2013. Why did blockchain.info accept this orphaned blockchain, why didn't it just discard it?
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.