Strange was about to say something along the lines of well, he had no idea that it was fae magic, that's all right, they'll try something else anyway, when Rita states that she'll at least try it. He follows Rita out of the trailer and to the open space. Then, Strange simply watches.

She manages to cast the spell nonetheless. And while Rita's awestruck, Strange is grinning like a moron. "I can!" he responds, with a little laugh. And he can also tell what it is. The magic is certainly Rita's, but there's something fae in there as well. Strange hadn't spent as much time with the Lord of Conflagration as he did the other fae, so he can recognize the essence of someone Summer Court, but that's about it.

"I can tell it's definitely your magic, though there's something fae in there as well." As he mutters something under his breath, Strange casts a small fireball as well, about the same size, which also forms in the air over an open palm. His magic isn't fae in the slightest: it's Strange's normal English magic that's powering the fireball.