Why did Mikasa pin Armin to the table in S4E14?

I hope I'm not missing some obvious answer, but I've always been curious about this. If it's true that there's no "Ackerman brainwashing" and Mikasa's feelings towards Eren are 100% genuine love, then what is up with the table talk scene? Mikasa clearly goes into a trance of sorts and protects Eren from Armin instinctively, before snapping back to reality and being surprised at her actions. Is this evidence that there actually *could* be brainwashing involved? Or just a small plot hole?