As to specific numbers, 10% seems too low to me--Wuhan is 6% of the population of Chinese cities at least as big as Wuhan, disregarding smaller cities entirely, including Foshan where the original SARS emerged, and disregarding Dr. Shi's expectation that origin closer to Yunnan was more likely. But at least we're within an order of magnitude of each other.
Knowing nothing whatsoever except that a pandemic emerged, what's your prior for lab vs. natural origin? It depends how you count, but we've had perhaps a dozen pandemics in the last fifty years, and one (the 1977 flu) was near-certainly lab-origin. So even with extreme optimism as to lab safety improvements, I can't see how you'd estimate less than e.g. 1%. For SARS-CoV-2, you'd perhaps adjust down for the novelty of the pathogen (since most lab work is with known pathogens--though most of the WIV's seems not to have been). It doesn't take that many p = 10% coincidences up to get to even odds or better, though.