What assumption? From the page you linked this is all that's said about the decision to add the Perplexity search addition:

Earlier this year, we gave you more choice in how you search by testing Perplexity, an AI-powered answer engine, as a search option on Firefox. Now, after positive feedback, we’re making it a fixture, rolling it out to more users for desktop.

How does this indicate that the "positive feedback" was from the forums? That seems like an assumption you're making here.