I noticed this as well. Reddit was the main service I used the forum search for, so if this was intentional, that would be disappointing, and I'll probably just go back to using site:reddit.com
(Although at the same time I've noticed that the Reddit results on the Forums lens was a bit unreliable, where it would miss some posts that appear in the main results, and sometimes ignore popular threads and instead show results from random bot subreddits, especially for political results.)