the correct interpretation of this requires seeing a related tweet where A-chan was given a very large bust. compared with that, then, this artist drew her with a normal-sized chest, or more "true to form", if you like.
A-chan's tweet here, therefore, should be read more along the lines of "you didn't have to do this", with some kind of pouty/grumbly intonation.
Less "Not considerate" and more "you shouldn't have concerned yourself with making my chest flat" as a tongue-in-cheek/joking kind of comment
