There is a difference between a quick passport check (or even a slow one) and looking through a passenger's device.
You're assuming it wasn't a UKBF device just like the one which was used to scan my passport upon my departure on the Eurostar at St. Pancras in December. Passport reader attached to a handheld device. If it's anything like the devices I'm familiar with it can be used to query databases and peruse passage and travel history.