So far in 2014, ProFootballReference.com. Daryl Turner, in 1985, posted 13 touchdowns on 34 receptions, which was the highest touchdown rate (touchdowns divided by receptions) among the entire group (38.24%). As of today, Thomas' 37.5% touchdown rate would rank second.
You'd automatically assume regression with numbers like this, and that's certainly possible (or probable). But his body size in the red zone and Peyton Manning's tendency to look for him there is the reason this is happening, and until teams can stop it, the Broncos will keep looking Thomas' way.