No because the EU forced them to actually allow the browser engines. It turns out that somebody with an actual brain was behind the policy decision.
Shockingly it turns out that despite what apple always claimed it was actually perfectly possible and weirdly isn't actually a security threat after all, who knew.
I don't think people can develop a browser engine that fast, and apple is still scrambling to figure out the least amount of compliance to avoid legal trouble.
So I doubt they are using a different engine at this moment.
I think porting it to iOS still probably takes time, but I am happy to be proven wrong if you have source stating that brave is not using webkit on iOS.
The porting has probably already been done, as sideloading apps, while difficult, was still possible. It'd make sense to have something waiting in the wings, so to speak. So it's doubtful iOS development has just started.