lol she's so cute >.<

Maybe because she's talking about "artpop aliens" not ARTPOP (the album) ;)

"ARTPOP" is a title ; "artpop" an artistic current.

Cuz she is LADY GAGA and can do what she wants! There, problem solved!!!

used like description

she's probably just being lazy lol

Really, she's talking abouts arpop aliens... They aren't albums.

ARTPOP: Album

stop to be stupid little monsters -.-

"artpop" is working as an adjective in the sentence, I guess it's OK not to capitalize it.

i think gaga is drunk. ALWAYS. #DrunkyGaga ♥

This is what I think: What she meant is when you draw a cover of album, write about the album or design a tracklist for the album write ARTPOP instead of Artpop. In regular or instant texts, it isn't necessary to capitalize.