It is the output shaft speed sensor. Not vehicle speed but output shaft speed.
The wrong sensor, which they ordered for you does not even go on the transmission
Chrysler also calls the vehicle speed sensor something like "distance" sensor but the confusion should have been eliminated with using "output" vs "vehicle" speed sensor.
I think aftermarket might call them "transmission speed sensors" its still not "vehicle speed"
I can be kind of an *** about stuff like this, but I would tell the parts guy to take it back one way or the other. He is the one that ordered the wrong part. They can take it back, they just dont want to. You could always keep it around for a spare though I guess.
I dont know if this link will work, but I looked up the correct part at O-reilly's. You can have your parts guy try to get this part number or see if he can cross it over too.
Dorman Part # 917-602