Ultimately, no I dont think it was on purpose. Though there are some scenarios where it would make sense but personally I dont see enough evidence to support those scenarios. I doubt it was even accidental release.

If it was on purpose, then it was likely supposed to be a bioweapon. But it affected the country that the biolab functioned in REALLY badly. So unless the purpose was to cull the population there and maybe use that as cover to cause damage to rest of the world too I dont think it was on purpose. Also I doubt china would let foreign controlled viral biolab exist, so foreign influence is also quite remote possibilty. Foreign sabotage is plausible though but there is no way to even speculate about that. But if that was the case, i think china would be much more irate about things(and i dont think anyone could pull something like that without leaving ANY traces for chinese intelligence agencies to even suspect).

So the on purpose scenario would require that complete psychopats with taste for blood are in charge, accidental release of bioweapon scenario would mean complete idiots are in charge. One would imply more would follow, another that either idiots are no longer in charge or also more would follow.

There is also possibility of commercial reason; develop a virus, release it and sell cure for it. I think the "shareholders" wouldn't let the disease to fade away this much, or become more mild. I'm not sure how fast they did develop vaccines for it though. If its simply not possible to go from 0 to something that can be distributed to masses so fast, then some work would have had been done even before the outbreak. But I think there would have been at least some hints at some point, cant keep stuff like this 100% secret forever.