The diagram and documents specify the NEMA17-400, which is certainly the 0.9deg (360 / 0.9 = 400) motor, but confusingly the serial number ends with X2 which is the same suffix as the 1.8 (200 step) motor. The serial number as shown is: "42BYGHM809 L20P4.5-17-X2" so it's literally just the "2" that appears spurious in the description.
Yeah I wouldn't go by the serial number. Check the degrees 1.8 or 0.9 Or to make it even easier the short ones are the z axis the rest are all the same
