The main problem here is that kiss magic is a narratively sensible solution to Strange. After all, he's specialized in disenchantment via his mouth. So probably to everyone's surprise, Lambert's smooch attempt slightly works. Of course, the key word here is slightly.

Now Strange has two competing influences in his brain: most of him wants to stay with Ignatius, while a tiny part of him wants to go back to the carnival. Something's definitely shifted in his posture. He's still tense, but it's more like the tenseness of a cornered cat than the battle-ready tenseness he had before.

He's certain of one thing, though: he is way too straight for this kissing nonsense. So, Strange attempts to bite down hard on Lambert's bottom lip while trying to push Lambert's face away with his hands. This means that Lambert's getting some claws to the face as Strange does so.