Makes perfect sense.
If the Lions lose, they will be 9-7. If the Redskins win, they will be 9-6-1. The Redskins record would be 1/2 game better than the Lions, therefore,
the Redskins would be in the playoffs.
Now if they Redskins lose, they will be 8-7-1. If the Lions lose, they will be 9-7.
The Lions would be in the playoffs by being 1/2 game better than the Redskins.
However, if the Lions tie, and the Redskins win, the Packers win the division (they would have a better division record than the Lions), and the Lions will be the wildcard team due to the fact that they beat the Redskins head-to-head, and both teams would have identical 9-6-1 records.
What's so difficult to understand?