They definitely have lots of signs that say this.

However!!!! It is quite the scam. It makes it seem that they guarantee prices are cheaper at the airport than downtown.
But look at the T+Cs.. https://www.hongkongairport.com/eng/...guarantee.html

''If you have bought any item at Hong Kong International Airport and found that the price is higher than that of an identical item at our retailers' comparable outlets in Hong Kong operating under the same Trade Name on the same day,''

You then have to apply in writing to state the difference in price. Wait for a response and then RETURN the item in its original condition/ packaging.

I'd be surprised if anyone had got something from this scheme.