I'm not an expert, but it looked to me that in the second half, Clement wasn't just dropping three steps and firing. He was actually having to look for receivers, and even in the first quarter, he really never would have had time to do that.
That leads me to believe that the secondary was actually covering people - and the great thing about a good pass rush is you don't always have to cover every option for the entire play, if you can take away that first option, a lot of times you've done your job.
So personally I thought it was a combination of better coverage and a worn down Rice OL.