Is that a polyester tooling gelcoat on the mould?

No, it is vinylester.

Are you certain? I've only ever seen that green in a polyester.

That is definitely a release failure is why I'm asking.

I'm not sure what it is, but at least it was supposed to be vinylester: https://composite24.co.uk/gelcoats/vinylester-tooling-gelcoat

I don't know if it matters, but first I applied gelcoat to this mould too, but since I saw that how difficult the layup was I decided to remove it. I was very easy remove with fingers. Then I layed up the carbon fiber, without applying more relase agent before since what I understood, it isn't needed every time. I used this relase agent: https://www.jacomp.fi/wp-content/uploads/2017/12/marbocote-227-v6.pdf