Board Thread:Episode Discussion/@comment-30530552-20171121182355/@comment-24994749-20171121215804

PisceanWaterbender wrote: the only way I see Qrow confirming Vernal is there is if they happen to mention the random lightning strike. And even then, considering how difficult it was for them to accept magic's existence, they might attribute it to Semblance. Vernal was the bandit to interact the most with Weiss & Yang, so I think that when the girls recount their experience at the camp, they would bring her up by name. And Qrow should know the Spring Maiden by name.

So even if Weiss & Yang didn't make the association that the lightning strike = magic, they are likely to rely the information to Qrow.