If the two denver players pushed down on Dreschers back, surely isn't that a block in the back or holding on the defense?

Read this you guys, these are the altered rulea for the 2016 season

Goal/Extra Point Rush Tactics

Game officials will monitor and strictly enforce the rules pertaining to illegal acts committed by the defensive team while trying to block field-goal and extra-point attempts during the 2016 season, including:

Making forcible contact below the waist of offensive blockers.
Grabbing an offensive blocker and pulling him to the side or toward the ground to create space or a gap for a teammate to rush through.
Using the hands or other parts of the body to push off an offensive blocker to gain leverage in an effort to block the kick.