Not much to the story. The server wotbase.ru released an info, that the Sturmtiger is being supertested, alongwith this picture:
It's a fake.
My contact confirmed no such thing is being supertested. Additionally, screenshots from supertest contain watermarks, visible when the picture is blue-shifted in photoshop to identify leaks. This one doesn't have it. Most likely a changed model. Same goes for the "E-25".