1: why is it a conspiracy that your player would have been sent off but theirs was not. What inference are you putting on the referee here? What was the point in making that statement other to detract from the credibility of your point in general.
2: does not matter if the tackle is from behind, side or front, if it endangers your safety (which is different from having a complete disregard for your safety), that player goes. The propensity for injury is higher for a tackle from behind but that's it.
3: as it was from behind as you say, you are unlikely to have full optics of the tackle so how are you placed to describe it? What are you basing it on? Was this what someone told you or from a video clip?
4: you never mentioned the force and speed used, if the player was airborne or lacking control in making the tackle and point of contact (low or high) - all key criteria
5: if a referee has the colour orange in his head (unsure if yellow or red) FIFA have changed their coaching as of two years ago that you go down to a yellow as opposed to previously where you went up to a red.