My question is: Was the controller correct in this situation to use the phrase
"descend at your discretion."

Thanks for your thoughts.

Matt

It's not a matter of whether he was correct or not, he just gave you
the option of staying at your present altitude or descending. At 7
miles out you'd just continue on the assigned heading until switched
over to tower who might then have you join the left base or make a
straight in approach. Asking if you were cleared for the visual was
just a minor gaffe on your part - I've heard and done worse. Sometimes
you'll be surprised what you'll hear when expecting something else.