Is this Texas Holdem hand a misdeal?
No, the hand is not dead.

Looking at Robert's Rules of poker here the following is included in rules for misdeals.


  In button games, action is considered to occur when two players after the blinds have acted on their hands. Once action occurs, a misdeal can no longer be declared


As action has occurred (players calling pre flop) then this rules that the hand can not be declared dead.

I'm confused as to how the top few cards would get mixed up but as long as they haven't got mixed with the muck (previously folded cards, or discard pile to boardgamers!) then the cards coming off the deck will still be random and continuing is possible.