They deem it to be a goalscoring oppurtunity when the last man fouls him.
The last man rule may not exist but if the LAST MAN fouls him then denies that oppurtunity, hence the LAST MAN is sent off.
The two "rules" go hand in hand, they are the same thing, because naturally, any LAST MAN would DENY a GOALSCORING oppurtunity by fouling someone running through on goal, wouldn't they?
They are not two different rules, at least i never saw them as such.
And Kosy was the last man, he fouled Ranger, who was running through on goal, with nobody covering...Denying a clear goalscoring oppurtunity...
Even though personally i thought he dived.