[Taxbilly]

Those sound like "woos", not "boos". What gives?

It depends on what "sound like" sounds like.

[Lexinom]

Unfortunately the limitations of prose force an explicit explanation for what is clear listening. A "woo" begins at and attains a higher pitch than a "boo". A "boo", uttered collectively by a crowd, starts low and progressively descends in pitch.

One may have had difficulty, rescued only by the context, distinguishing between a "boo" and a "Moooo"kie Wilson or Isaac "Bruuuu" chorus. I've never had trouble, however, separating "boos" from "woos" because of aforementioned pitch differences.