Game Wins:
3 vs '06 Pistons (64W), 4 vs '07 Pistons (53W), 3 vs '08 Celtics (66W), 2 vs '09 Magic (59W), 2 vs '10 Celtics (50W), 4 vs '11 Celtics (56W), 4 vs '11 Bulls (62W), 2 vs '11 Mavs (57W), 4 vs '12 Pacers (52W*), 4 vs '12 Thunder (58W*), 4 vs '13 Spurs (58W), 4 vs '14 Pacers (56W), 1 vs '14 Spurs (62W), 4 vs '15 Bulls (50W), 4 vs '15 Hawks (50W)
49 Playoff Wins vs 50-Win+ Teams (out of 113 playoff victories)
Series Wins:
'07 Pistons (53 wins), '11 Celtics (56W), '11 Bulls (62W), '12 Pacers (52W*), '12 Thunder (58W*), '13 Spurs (58W), '14 Pacers (56W), '15 Bulls (50W), '15 Hawks (60W)
9 Playoff Series Victories vs 50-Win+ Teams
8-2 in last 10 series vs 50-Win+ Teams
*82-game equivalent based on 66-game season
In 10 postseasons he's squared off against 15 50-Win teams. That doesn't sound extremely low to me.
The stat was shown during last nights game and didn't include this season, since it isn't over yet. So, it wasn't a "vague stat that makes no sense."
However, it is a misleading stat that doesn't take into account that Lebron's team can only beat the teams in the playoffs that get there. He has no control over how many wins it takes those teams to get there.