By my understanding "casual blood pressure" is when you sit for 5 minutes in a doctor's office then have a blood pressure measurement taken [1]. "Ambulatory blood pressure" is when a monitor is strapped onto you and automatic readings are taken periodically (typically half hourly) over a period of time (typically 24 hours) then averaged.
There is some debate (according to Google), but diagnosis of hypertension typically involves an ambulatory measurement over a casual measurement. It strikes me that the ambulatory measurement is the more important one from a long term health perspective, and it's odd that the paper chose not to mention the ambulatory measurement along with the casual measurement, though I'm not a medico.
As an aside, at one point I added a microcontroller to a cheap Aldi blood pressure monitor to do ambulatory measurements. A doctor seemed keen to diagnose hypertension based on a few casual readings, but I was keen to base the diagnosis on more data.
