There are several factors. Modern drivetrains are less tolerant than older 6/7-speed stuff. There's a good chance the shop is recommending replacement based on the newer intervals, which are as low as 0.5%.
Park Tools recommendation is replace 0.5% replace immediately for 11/12 speed and 0.75% replace immediately for 9/10-speed.
Chain Wear Indicator | Park Tool

Secondly, make sure the chain is taunt when checking, by pressing on the crank (it looks like you did this).
Third, there's some level of manufacturing tolerance to all chain checkers, and tests should be taken as approximate not absolute. Measuring with a 12" steel ruler will tend to give a more reliable (although significantly slower estimate).