In all likelihood Lemmy has lost a lot more than that. The older lemmynsfw.com struggled to report its stats for a long while so I am not sure how well those MAUs are represented in the total Lemmy counts, but when looking at them directly it's gone from 3335 MAUs in August 2025 down to 161 in August 2026, which is nearly twice the number you mentioned regarding Lemmy's loss and that is merely one instance.
Also I don't see lemm.ee anywhere in the Fediverse Observer either, which probably means that the total Lemmy counts today include none of their subscriber numbers from before they shut down? (I suppose it would depend upon how those are calculated - among all known, current instances, including their pasts?) And it was a top-5 one too, along with Lemmynsfw.com that iirc might have been #2 after Lemmy.world (which tracks given the numbers I mentioned earlier and current subscriber counts, e.g. what that site refers to as the current #2 sh.itjust.works has a mere 2296 so is half again smaller).
Then fedinsfw.app's MAU gains correlates well with Lemmynsfw.com's loss, while Lemm.ee's demise spread people out more to multiple instances.
Though the Threadiverse overall is still shrinking. We used to have sth like 65k at the peak after the Rexodus, or you might say more justifiably a more stable 55k, vs. today's "mere" 35+7k. And Mbin has ~1k MAUs total, half on a single instance.
You could argue more activity I suppose, or more enjoyable style of posting or some such, but I don't see the Threadiverse growing, I see it shrinking, even if the rate of loss has lessened as of late.
PieFed has exploded though within the past year, yes. Even if that does not match the rate of Lemmy's longer-term decline.