I think that I played vs a semi-abandoned team, what means that he have players out position because the contracts of players he had, expired, so the sub's went to occupy the empty spots inside the main 11, and these sub's were from other positions...
I doubt that he was tanking just with a 2nd Gk as dmc and a Mr as DR dont have negative impact.
Then tanking basically, is when you set up a "bad-illegal formation" to lose matches with the idea to don't promote.