calling a piece of 3d art a painting to many isn't a technicality. the ones who questioned it as a painting still had good things to say so i'd discount them as bad comments. on the whole i'd say they weren't nasty. i can understand how you feel though. 

why do you wonder if you're an artist or not. why is your desire to make art eroded? forget about what you or others think  you are and do what you enjoy doing. i'd have to use poser for ayear to do anything as good as your pic. is it art , isn't it art does anyone really care. ask yourself this...did you enjoy doing it? are you pleased with the outcome....will you do better in the future.
if your answers are yes to these three questions then you're a lucky person who has a lot to look forward to. we can always take something positive from something negative. you actually made a couple of people  who don't care much for poser work say well done. all be it they said they didn't like poser work first but think of it. you got them to say something positive.  i think the lens flare comment valid so you can take that and turn it into a positive. with that comment in mind you'll prob try and refine the flare so it's better if you use it next time.

just grow a thicker skin, accept that not all negative comments are bad and carry on enjoying what it is you do....and stop questioning if you're an artist or not. question what you do not what you are. jmo

billy