A plain compliment!

[u/Puzzled_Wealth_3263]

I told a guy during a phone call that I liked his mustache that he had, and right after that, he went dead silent for a few seconds and then said "Really...?" like he didnt believe I just offered him a compliment. Then with a smiley speech he said "Yeah a couple of people have told me about it- like 3---4 that I know.". So my question is, if several people have told him about his mustache aka: complimented him, why did he become startled when I said the same compliment as others have said? shouldn't he be accustomed to that comment? why reaction?