I never said that, as HC, I'd opt to take a knee. But, you can't argue that it's more risky, however incrementally, than handing off to a RB. Snap to the QB, he waits a count or two and kneels. Clock runs for 40 seconds down to roughly 15 seconds left. You punt (you could punt it OOB on purpose to eliminate the runback possibility or pooch kick it so it rolls and rolls and burns even more clock, which WA did NOT do). The likelihood of TX executing a 75 yard drive with no timeouts in 15 or less seconds is infinitesimally small. Not one fan would ever question your decision if you decided to take a knee and burn clock. OTOH, I'm sure there are WA fans today who have wondered why did they run that last play into the line and, unfortunately, give TX an additional 40 seconds to operate due to the injury? And, they still had to punt so that part of the equation is no different whichever option you choose. It's all about burning as much clock as possible. Also, IIRC, it was 3rd and about 8 with TX bringing everyone so the likelihood of picking up the first down running off guard was also pretty slim.
It was a weird situation that penalized WA. In 99% of these situations, there isn't an injury and the result is the same either way. IMO, there is more risk, however slight, in executing a handoff from QB to RB than for the QB to just kneel.