False Advertising Or Faulty Understanding?

I’m a manager at a shoe store. Today, I was working at the cash register. An old lady brought up a pair of sandals. With it being July, our summer clearance sale has begun with styles anywhere from 20% to 80% off. These specific sandals were 40% off; the sale price was at $35.99 and the full price was $59.99.

I rang up her shoes and checked them — a company standard our chain has to ensure that the shoes belong in the box they were brought up in, are the same size and style, and have no visible defects. The lady handed me a coupon for $10 off a purchase of $59 or more.

Me: “Oh, I’m sorry. I can’t use that coupon as your total is $35.99 since they are on sale. The total has to be at least $59 for that coupon to be used.”

Old Lady: *Looking confused* “Well, that’s just false advertising.”

She paid for them anyway, but the whole time, I was thinking, “How the h*** is that false advertising?” The shoes were on sale, and the coupon stated the requirements for use. I honestly don’t even think the lady even understood what false advertising really is.