Yes, that's exactly it. HR is the wrist pulses. That said, for an accurate use of the pulses, it is currently recommended to use the belt. And honestly, in January, CES will be held in the USA -> presentation of new electronic products, Gramin could release the Fenix 4 or other novelty, whose accuracy and reliability HR on the wrist should be improved. It's up to you to see if you can wait.

Probably the WHR version has an integrated heart rate monitor on the wrist, whereas this one works with a cardio belt (much more reliable than the wrist measurement)