If it came from somewhere else, why wasn’t the outbreak noticed there first, is the million dollar question. It requires some serious mental gymnastics at this point to believe it didn’t originate in that lab. The only real question is if it was released deliberately.
Sure, China has way more public health capacity than it used to, but we know that COVID can spread silently in a community for a month without anyone noticing, even when we are looking. It happened in California and Seattle in January 2020. Why wouldn't that have happened in, say, rural China in October?
If you take an unknown diseases with an R of 2-3, what you will see is a number of smaller clusters, some dying off, before you get the one cluster that becomes the pandemic.