It was only the tenth time EVER that Iowa had beaten Michigan. I don't blame them for rushing the field. National TV game against a traditional power (unranked or not) is big. If this was Minnesota hosting Michigan last Saturday and we beat unranked Michigan in an ABC national prime time game at night re-claiming the Jug, I'd have rushed the TCF Bank Stadium field.
And, as others have said, it is an every game routine there. No big deal. I've been on that field, too, and it is kind of cool to see what it is like.