You don't need to apologize for borrowing a pose and an outfit from an outside source for FANART. It's obvious that he did not trace the work, simply copied it and he made no move to hide it either, going so far as to reference the pose for his next piece as well. There are, frankly, HUNDREDS of better ways to suggest to someone that maybe they ought to give a different outfit or pose a try or even to ask if maybe they referenced something in the first place, but you've gone beyond the realm of friendly discussion into malicious belittling.
If someone wants to become a better artist then yes, they OUGHT to copy from other places. Not trace, but copy. This is what we do when we draw from real life, is it not? It's the same when we copy a piece of 2d art as well. If you copy a GOOD work it will help you understand a lot about translating an outfit into 2d, in even the smallest things, like noticing how a pair of pants puckers under the hem of a shirt.
If someone wants to HELP someone become a better artist, putting them down is NOT the way to encourage them.
If someone wants to become a better artist then yes, they OUGHT to copy from other places. Not trace, but copy. This is what we do when we draw from real life, is it not? It's the same when we copy a piece of 2d art as well. If you copy a GOOD work it will help you understand a lot about translating an outfit into 2d, in even the smallest things, like noticing how a pair of pants puckers under the hem of a shirt.
If someone wants to HELP someone become a better artist, putting them down is NOT the way to encourage them.