From what I understand, the person who asked the question implied that the compliment receiver inwardly believes the compliment but outwardly denies it, indicating that there is a deceitful connotation.
While I think that superficial is a stretch, would ostensible not be more suitable for the case?
Dave(who thinks it's pretty good himself): Nah.. The hairdresser should've done a better job on the sides.
It can be said that Dave is acting ostensibly self-deprecating thus Dave can also be described as ostensible.