He was believed to have cost that by a single source. Why people take a number posted by the media, not even as a fact, and then let it become a fact after that I don't know. It only takes one media outlet to say a number. The rest will run with it and it will stick unless club officials say something (which they hardly never do).
It might have been 10 million. Might have been 12. Might have been 2 million and then 1 million after 5 or 10 or every 5 or 10 games. Might be the reason why he didn't play at all if that was the case.
He was a shit transfer no matter what the fee was. The higher the fee, the slightly more shit it was but it hardly matters at the end of the day.