Strange doesn't say anything as he watches. However, based on his expression, he's obviously proud and very impressed by Yuya's work.

And yep, he does follow. Just a moment or two later, Strange appears in Yuya's room via Yuya's mirror. He's giving him a huge grin, super impressed by all this.

"This is what I'm trying to tell people! You managed that magic because you took my framework and made it your own. Yuya, I'm so proud of you."

This is what he's been trying to tell Lambert. But hey, it counts.