No, no live plants in those tanks except for some lucky bamboo, and IMHO that doesn't qualify as an aquatic plant.
Actually he probably tested, but if you test with the wrong kit (as in use low range pH tests on hi range pH water), you might as well not bother.
I've always asked what pH stores keep their tanks at. Most here on the freshwater side only adjust the pH for discus. But this was the craziest discussion I ever had over local water. BTW our water should be about 7.8 to 8 out of the tap. Since it is city water I can get detailed water reports.
Well anyway, yeah, it's a fine line sometimes to gently educate your learning customers while not talking down to your educated customers. One phraseology that works is, "While there are many ways to (blank) I've found that (blanking) this way has worked best for me or best for us here in the shop." Or, "over the years we've had a lot of success with (blank)" and "Though you can do it that way, we've had more succes with (blank). I can tell you more if you'd like to try it"
There are many ways to treat your customers with respect even when they may need to be educated.