Count the grooves on the crown.
8-9 grooves small crown.
Original bigger crown should be 11-12 grooves viewed from that angle.
It is also common knowledge that once the watch have been sent to service, the crown is the 1st part that gets changed.
I have no idea why they choose to replace the original bigger crown with a smaller one. (trying to steamline parts stock maybe?)
But as long as it is an original Zenith crown, it should not be a problem.