User blog comment:XGlass Reflection/Ep & Ch Review~ People Die When They're Killed!!/@comment-24173229-20130909222709/@comment-7418318-20130909224956

Rather unlikely.

When Hannes brought Eren and Mikasa to the boat Armin and his grandfather were already on board together and quite far to the front of it too, which means they probably boarded a few minutes before.

It's unlikely that Armin could calmly have eaten Carla, then transformed back into Human form, meet with his grandfather and still arrive at the boat a few minutes before Hannes, Eren and Mikasa.