I am not sure this is against the guidelines. I don't think it's illegal to post it, but then there are some illegal numbers: https://en.wikipedia.org/wiki/Illegal_number

However, the commenter might have just posted the magnet link, which is more to the point, and unlikely to disappear (torrent 2.0 notwithstanding), unlike some third-party website (which could also turn out to be an infection vector). It also shortens the trust chain.

magnet:?xt=urn:btih:3d8b16242b56a3aafb8da7b5fc83ef993ebcf35b&dn=Microsoft%20leaked%20source%20code%20archive_2020-09-24&tr=http%3A%2F%2Ftracker.opentrackr.org%3A1337%2Fannounce