The author appears to have the honest intention of analysing this question as thoroughly as possible.
If there is some other website or paper that goes through this in more detail, it would be good if someone could post a link to that website.
It could be that next week someone discovers the intermediate host (like the civet cat was for SARS), and the whole discussion becomes moot. But for the moment I think we are still in "don't know either way" territory.
Also we may eventually come to a deeper understanding of the nature of zoonotic events, and whether it is at all possible that a scientific laboratory could accidentally become part of the chain of transfer.
For example, it might be that a coronavirus only rarely and temporarily exists in a state where it infects the source host and is capable of infecting the destination host. In which case such a transfer will only ever occur in a situation where large numbers of indidivuals from both source and destination species exist, ie in rural areas where wildlife mixes with people, or in farms, or some combination of those two.
Another thing I would note is that all the examples of laboratory accidents were of organisms already known to be dangerous human diseases. Those types of accidents can and do happen. Whether it is at all probable that such an accident could generate a _new_ dangerous human disease is not so obvious. This comes back to the question of what probabilities are involved in the events leading up to a typical zoonotic event.