Yes, but I add a little detail here.
It´s similar to "they are like" (eles pensam! /eles dizem/ eles agem ou ficam "tipo''). So, the reaction can be on the mind realm - "they think" or a reaction "they say" (metaphorically or an actual reaction in which they state ''I don´t care".
Anyway, what matters to the author of the sentence is the reaction to his/her statement "Buying books online is better'', so he is making a contrast, as though he/she is wondering why they go "I don´t care" (to him/her is a no-brainer - or it seems).