It’s actually a fascinating bind Steve/Reddit has put themselves in. Because it is a non-exclusive license, you can affirmatively declare your content is free for anyone to scrape or use.
After that, if Reddit ever asserts rights over your content by, say, suing Microsoft for improperly using your content in training data, you now have a legal claim against Reddit for interference with either your ownership rights or with a contract via whatever license you have made your content available under.
Now, maybe Reddit has a claim release in their TOS, but it wouldn’t prevent you from getting an injunction enjoining Reddit from restricting your data from being used by Microsoft.
It’s kind of academic, because… it’s not really a victory that Microsoft is also training its AI on your data. But, hey, they’re probably doing it anyway and at least this way we get to screw over Huffman for being an ass.