the tech told me that the front brakes looked great, but the rear pads were getting pretty thin. Is this normal?
Perhaps for a tire shop but I normally wouldn’t recommend replacing brake pads @ 5 mm thickness.
Your front/rear brake wear (6 mm front, 5 mm rear ) is quite even. New brake pad thickness is usually 12 mm for front pads and 10 mm for the rear pads so your brake pads are worn to half of the original thickness but less than half of the usable material remains. The minimum pad thickness is usually 1 mm but replacement is often recommended @ 3 mm to avoid an unscheduled service visit. If your wear sensors begin to rub 500 miles before your next service visit (oil change) your reaction might be to stop at the nearest brake shop instead of your usual shop.
If you have your vehicles maintenance performed at a full service shop they will normally inspect your brake pads and tell you when the pads measure 3 mm or less. You might get 20,000 more miles from your front and rear brake pads.