To leave it at that means to take no further action or say nothing more about something, and in this context the speaker is saying they weren't stupid enough to leave it at that or stop without taking any further action.
Context: Looking out the peephole showed nothing, but I wasn't stupid enough to just stop there and take no further action.
Hypothesis: Looking out the peephole showed nothing, but I wasn't stupid enough to leave it at that.

Is the hypothesis incorrect? (Yes, no, or unknown)?