leewiART is the name of a website very similar to deviantART where many artists post their work; it is not an artist's name. I have several pieces by this artist in my collection under the name xiaosa - a name used to display the same artwork found in this DA gallery on CGHub, which recently closed its doors. Because CGHub closed, it makes sense to me that this artist would choose to set up an account at a replacement site (in this case, DA). Many artists seems to use different names on different websites, so that alone does not seem to indicate the artwork is stolen. The fact that the gallery contains the same works here as it did on CGHub and on leewiART, etc. also indicates to me that this may very well be one artist using a variety of user names. I believe you may be incorrect in your accusation of art theft.
Also please explain to me why this piece bennidi11.deviantart.com/art/H… could not be found using tineye reverse image search. It's either: 1) the artwork was not indexed for reverse image search using that particular service 2) the artwork was submitted by its ORIGINAL ARTIST You can guess which of these is more likely. If this piece I linked was stolen, it'd be somewhere on the internet as well.
And the possibility that it was stolen from another artist is extremely unlikely because that artwork matches the art style with the rest of this deviant's gallery.