Whinge session

Yesterday I was asked by my boss how many sets/reps I had an overweight client doing. When I replied 3 sets of between 10-12 reps the look of horror on his face was priceless!! This is how it went:
Boss: How many reps you got her doing?
Me: Between 10-12, depending on which exercise and a lot of supersetting with cardio in between. I try and keep her heart rate up for the whole session.
Boss: WHAT? HOW MANY?? Why on earth would you have her doing THAT??
Me: Um, so she can build some muscle and strength so she can raise her metabolism and burn more calories.
Boss: No, no, no - not good. She is a big girl, you dont want her to bulk up. Make her do about 16 or 18.
Me: But she's not a beginner, she's been lifting weights for yonks!
Boss: Trust me, she'll put on weight.
Me: Uh, OK, whatever you say, you're the boss. (Secretly plotting how to make him think that I've taken his suggestions on board)

Is it just me or is this completely ridiculous? I've been lifting heavy for ages (3 sets of 8) and I havent turned into Arnie! Shouldn't he know that women dont "bulk up" that easily. Ok, I know she has a lot of weight to lose, but she is freakishly strong and it took me ages to build up to the weights that she's doing. Somebody tell me I'm right, pleease??