Not true. Check the second INT by Burnett. 4 men in downed stances, 4 men rush the QB. Not blitz. The majority of Colts final drive is this way as well. 3 or 4 down linemen with no pressure from the DBs or LBs. Dallas has often played conservative football and rushed only 3 down linemen out of the 3-4 this season, as well as last year.
The 3-4 defense is designed specifically to disguise pass rushers. While you are still often rushing only 4 men, it is still a blitz by definition. There is not a set number of men that have to rush for it to be a blitz by the definition of the term.