op return – Understand how ordinal numbers work in the Bitcoin blockchain. What exactly is stored on the blockchain?

It is believed that someone uploaded a Doom clone to the Bitcoin blockchain.

https://ordinals.com/content/521f8eccffa4c41a3a7728dd012ea5a4a02feed81f41159231251ecf1e5c79dai0

However, I’m a bit confused about what exactly is being uploaded using “ordinal numbers”. A quick reading of the Ordinals assumes you are using OP_RETURN and putting the encoded string into a block or transaction.

Is this uploaded encoded string an “id” that links to a file on ordinals.com? So technically no actual files are uploaded like this Doom clone? And if ordinals.com is offline, I can’t access these files?

And how is this different from the colored coins and counterparties of about 10 years ago?