The revenue from a few ads on the free tier in exchange for limited queries to GPT-5.3 is negligible compared to what they pull in from API costs and the subscription plans. This looks like a play to justify the existence of the previously money-losing free tier as they go into an IPO. Throw some ads in there to make it closer to a neutral on the balance sheet.
The key part of that quote was "everybody in the world". The ads are their way of sustaining the low end of the access.