The point is not that Gaddafi was a leftist, but that NATO is an evil imperialistic offensive organisation that overthrows governments
Of course Libya was never a NATO mission, was done by two countries (I include the UK as part of the USA at this point) that certainly could have coordinated even if NATO did not exist. France has always been the most NATO sceptical country in the union as well.
Oh and let's not forget that blaming NATO allows them to forget the real reason France got involved there. But why would they want to distract people away from Sarkozy and his neoimperialism? Let me check what's he got to say about Ukraine... Yup, checks out
Yeah my money is on the 60.000.000€ (IIRC) Sarko illegally got for his electoral campaign from Gadaffi (donations and such are very regulated in France and that was clearly very illegal), and then Gadaffi started to get vocal about it... ... and then suddenly he got caught bu French forces and oupsie daisy boom.