I'm going to go against the grain here and suggest the guy isn't trying to deceive - he just hasn't got a clue how to sell a car properly. As evidenced by the crap pictures and the odd way it's written for example 2.5 (si).
In pretty much all other BMWs the 'Sport' version is marketed as 'M-Sport' (which is what hes written) but for some reason on the Z4 they just call it the 'Sport' even though it's covered in //M badges anyway. So I can see a cause for confusion.
Doesn't seem a bad price either for a 2.5si Sport in decent colour/wheel combo.