It wasn’t just the bicep touching, but the overlong gazing into each other’s eyes, and Jaina’s guilty start when she hears the others coming forward, as if she’d forgotten about them.
However… I’m inclined to think this is (possibly unsanctioned) fanservice by the animators, a wink and a nod to the old-school Jaina x Thrall shippers. I think it’s very unlikely that Blizzard themselves intend for there to be a romance between the two.