It is unlikely that it was manufactured in the BSL. Apply Occam's Razor
What the hell is BSL? Anyway Occam's razor can suck whale's ass. Now you are coming with Hanlon's. You are using so many razors you are going to cut yourself.
But you are right, stupidity explains a lot of things. For example did the Chinese count on the US president's stupidity? He wasted a full month with the response, still wasting time with the ventilator at least a week. On the other hand other countries SK and Japan ac ting faster didn't get hit as hard.
If it was intentional, it was made by the Russians, my money is on them. You release this shit in other country not in your on backyard. And the virus itself is perfect, the host is spreading it for a week, it kills of the old, fixes social security.
But again, human stupidity can be the answer, read the Wired article from 7 years ago predicting the next SARS coming from bats.
Occam's razor says don't fuck with bats.