Oh no! So sorry to hear little Thor had this experience. Very glad to hear he was not hurt
We had a similiar experience a few weeks ago. The other dog was not a Yorkie, but a mixed small breed. After initially seeming friendly, it kind of "pounced" at Rem's face, nipping. Jack was with him, I was not, and he said he just scooped Rem up by his harness. The other dog had a bunch of Rem's beard in his mouth, but did not break any skin. Luckily Rem seemed unphased by the experience.
They do seem to bounce back pretty quickly... he is no more or less afraid of other dogs, but
we are a little more tentative when approaching new dogs now!