You're making a logical fallacy called affirming the consequent where you're assuming that just because the backdoor was caught under these particular conditions, these are the only conditions under which it would've been caught.
Suppose the bad actor had not been sloppy; it would still be entirely possible that the backdoor gets identified and fixed during a security audit performed by an enterprise grade Linux distribution.
In this case it was caught especially early because the bad actor did not cover their tracks very well, but now that that has occurred, it cannot necessarily be proven one way or the other whether the backdoor would have been caught by other means.