I have a few theories on that. scoville doesn't directly measure capsaicin, it measures how many times diluted you need to make a concentrated extract of the pepper before the heat is undetectable in sugar-water. So how it applies to sauces is unclear to me. You could take the scoville rating of the underlying peppers, or you could directly dilute the sauce itself, or you could somehow make an extract of the sauce itself and test that.

So maybe that rating is misleading because of ambiguity in how its measured, or the sheer quantity of oily sauce, its not like a little dab of vinegar-based hot sauce, it sticks