His knee AND elbow were down. Also, I've never heard that 15 yd penalty for throwing a challenge flag on an unchallengable play. I thought all touchdowns were reviewed in the booth?
Why isn't the play reviewable? What an absolute joke. Not only do the Texas get a TD they don't deserve but then the Lions get hammered with a 15 yard penalty.
Edit: Looks like the Texans benefit from a dumb loophole. The priority should be getting calls right, not a Nazi like enforcement of challenge flag procedure.