When he filled the glasses, he was filling the outside edge of them, not the cylinders, which had been filled with the same liquid prior to the trick. Each glass had a thicker cylinder, meaning the same liquid level could be achieved with the same amount.
Let me make it easier for ya.
Little Whip, watching him pour, he pours into the middle of the glass at times and it does not spill over a cylinder? Also, where did all the extra liquid come from to fill each glass back up at the end?