Using Techs on a Non-Tech class?

I had lost all hope for doing this, but I came across the following video of a Br/Ra doing an XH Elder Solo, and I definitely saw her use Resta in there. I tried to test that by buying an All-Class Talis, but I was still unable to cast it even though I put Resta on the weapon slot.

Video for reference: https://youtu.be/g8FFPvx2Ys0?t=298