Two different things...
People are looking for somebody to blame for a mess that has a LOT of blame to go around. I'm willing to entertain the proof that this is not a lab-grown virus, I think the forensics show this. I don't think we will ever disprove that this thing potentially escaped from a lab.
I would like to say it is monumentally irresponsible to have a lab that studies potentially dangerous viruses and bacteria sitting int he middle of any populated area. Even under the most strict hygienic standards, this is just a bad thing. There is never a need for such a lab to be located "near" any potential source, either, before anybody tries that argument. Yes, "boots on the ground" response teams, researchers who do the legwork, certainly, but biohazardous samples should be handled far away from any population centers. Even in the best case scenario, you get these conspiracy theories popping up, and in the worst cases... well.
Their conclusion that the virus has to pass from animal to human, is certainly valid, but assurances that the lab followed protocol? That's just rosy best case assumptions about the security that depends on a lot of factors, most importantly, that we are dependent on humans to uphold those protocols. People break rules, and it's not out of the question that somebody might have become infected due to a break in these protocols; COVID-19 is incredibly contagious, and we saw how poorly contact protocols worked for first responders in Washington who contracted it after evacuating a rest home that became the first "hot spot" - I'm sure their protocols were not as stringent as the Wuhan lab's protocols, but it does show how hard it is to contain this thing.
I personally hate conspiracy theories, and I love to poke holes in them through logic and accepted facts, but this one still has legs. Depending the infallibility of humans to follow strict protocols, who work a few miles from a "wet market" where livestock, both domestic and exotic, are kept in unhygienic conditions until slaughter, seems to be a stretch, at best.