If acoustic bothers y'all, then what does shred the gnarly do to you?
Of course technically acoustic relates to sound. But in the colloquial fads of hip talk, the implied meaning is relational. IE, acoustic guitar means non-electric guitar. Therefore the you have to think outside the box of some terms used. So non electric guitar and non electric bike makes perfect sense to be called "acoustic" when use colloquially.
Level of education has nothing to do with such phrasing when trying to be whatever the term is for cool person today.