Kdenlive is an old piece of software from over a decade ago. While we can't be sure that all of the contributors stayed AI-free, I'm sure all of the code was vetted for quality since a lot of people are invested in this incredible video editor.
Even from an anti-AI view, I'm not sure of what to make of skepticism like yours; what if vibe coders simply lie and say they didn't use AI? Then would you instantly give it a pass? Proof of AI-free work has become impossible due to offline FOSS models, so unless I'm missing something, all we can do is aim for quality and security by this point, I think.