This article clarifies why it may appear that opponents are earning points for bench players.

Any statistics earned while a player is in a bench position are not counted toward a team's score.

Your head-to-head matchup screen always displays the current lineup for both teams.

Stats appear next to a benched player's name if they were in an active roster position earlier in the week and were then later moved to the bench.

Since these stats were earned while the player was in an active roster position, they're counted toward the results of your head-to-head matchup.