I think "defined" would be a six (or more)-pack, washboard abs, while "athletic" allows for more leeway. I'd expect that an athletic swimmer would have more visible abs compared to a rugby player, yet both would be considered athletic. Body composition does change depending on a variety of factors, so someone's abs could look pretty different at different times of the day.
"Muscular" is all in the eyes of the beholder, and allows for a lot of interpretation. A bodybuilder looks much different than a CrossFiter, but both are muscular.
A provider's self description could be skewed by an intentionally exaggeration of their physique (overselling). Or they might have some body dysmorphia, so they undersell their physique.