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

Is it, if you don't share it further?

It probably still is, but I doubt that will really stop anyone here.

It's a torrent though. I thought about downloading it, but it seems unwise when you're automatically sharing it with others.

You can prevent it from seeding and delete the tracker after downloading. It's not nice to seeders but it's an option.

In what jurisdiction?

depends on where you live.