No, of course we are not "to believe" that. What we are to do is to consider it is a possibility. Or are we to believe that SARS-CoV-2 could only have emerged as a lab leak? Both the natural and the lab-leak hypotheses are feasible, but treating either of them with near certainty or as impossible is not justifiable with the current evidence.
Imagine an alternate universe where all events played out the same as in our own, with the exception that the Wuhan laboratory's existence was a perfectly kept secret by the PRC. In that case, would the emergence of SARS-CoV-2 in Wuhan lead to the certainty that there must be a secret facility nearby that specializes in novel bat-related coronaviruses?
To say nothing of the incredible coincidence of the WIV.
The natural emergence of a virus from an animal is much more likely than the existence of a secret, unknown research facility, but much less likely than a lab leak (particularly in the circumstances surrounding COVID19).
All these mistakes in reasoning that I keep seeing in these discussions is making me truly understand the definition of "gaslighting".