You're right, but I'm pretty confident that the difference isn't significant. We should probably see it as evidence that rationalists omnivores are about as capable as rationalist vegetarians.

If we look at average percent of positive predictions (predictions that earn more than 0 points):

Omnivores: 51%

Vegetarians: 46%

If we look at non-negative predictions (counting 50% predictions):

Omnivores: 52%

Vegetarians: 49%