Why are full lips considered an "ethnic" attribute?

And if they are, define "ethnic" in this context? Does it mean simply non-white, or just exotic but not pertaining to race or ethnicity? And why do so many people mis-stereotype white women as having such thin lips, when so many white women actually have full lips, take for example, Scarlett Johannsen, Angelina Jolie, Julia Roberts, Fergie, and Jennifer Garner? And I don't mean women with fake implants like Pam Anderson. Also, i'm pure white and people are always telling me how full my lips are (naturally by the way) and I hardly ever wear gloss or lipstick or anything ( I usually play up/decorate my eyes).