Probably this is the difference between 'chip' time and 'gun' time. Chip time is the more accurate measurement and is taken as you cross start/finish line from the chip in your number tag - this is the time you were texted. Gun time is the time from when they fired the klaxon (gun) to your finish - so if you started down the field and it took you 86 seconds to cross the start line after the klaxon sounded then this will explain the difference. (hope that did not sound patronising!)
Incidentally - I've never known such instant texting of results before - I had mine almost as soon as I crossed the line.
Was available really quickly. I didn't think of looking for a text to tell you my chip time!