The Chargers are 5-1 while the Chiefs are 2-3. Not many 6-1 teams end up missing out on the playoffs so that would be significant for San Diego, not only for their overall record but also knocking the Chiefs back three and a half games in the division.
A win by the Chiefs would give Kansas City new life, especially with the schedule softening up in the next few weeks. It would also keep them reasonably close to the Chargers in the AFC West.
FiveThirtyEight has a cool feature that shows the playoff implications for every team and every game in Week 7. It shows the biggest swings for a team's playoff chances for each game depending on who won or lost. The Chargers and Chiefs are No. 1 and No. 2 in the AFC with the biggest potential swing in playoff percentages with a win or a loss.
Obviously the numbers aren't everything. We don't know what will happen which is why the NFL is so fun. But if you thought this weekend's game was a big one for the Chiefs playoff chances, it appears you are correct.