McCarthy thought Pope was out of bounds - NFC North Blog - ESPN. This missed opportunity by Mike McCarthy was hardly the reason the Green Bay Packers suffered their first loss. But this would have given them a much better chance of pulling off the come from behind victory.
McCarthy made a good point. It was a very close call, and based on the information they had available to them at the time, they didn't think the play would have been overturned. But he should have challenged it anyway.
The situation required a challenge. It's the fourth quarter, they're losing, and it was likely the Chiefs would score at least a field goal if the play stood. Even if he thinks it's a close call, or not likely to go in his favor, so many NFL rules are subjective that he could have gotten it anyway. On the replay, it sure looked like it would have been ruled a fumble and a touchback.
This isn't a criticism of the refs for missing the call. It happens all the time. And it's why coaches have the challenge flag. Maybe McCarthy just isn't used to playing from behind late in the game, but he should be more aggressive with his challenges in pivotal situations like that one.