Likely it was still fermenting a little bit and that's how it carbonated. The white vapour you saw was probably condensed water vapour from the sudden pressure change, although I'm too lazy to dig up a textbook to confirm this for sure...
Even though the JAO directions don't SAY to stabilize it before bottling, carbonation is always a risk when you bottle ANYTHING with residual sugar. Out of 40 batches of JAO and JAO-based variations, I have so far had two that kept going after bottling. Which is why I always bottle anything unstabilized and still sweet in those swing-top bottles or screw-top bottles so I can check on them a few days and then every week for a few weeks after bottling to make sure they aren't getting pressurized.
Is the rest of this batch bottled or still in a carboy under airlock?
If it's bottled, I highly recommend you refrigerate any other bottles from this batch and then pop them open to let some of the pressure off... the refrigeration will significantly slow any further fermentation and if you open them cold and then let them warm up, they're less likely to erupt all over while they release their carbon dioxide.
If it's still under airlock, I'd recommend you give it a few more weeks and maybe a few thorough stirrings.
Racking only removes the yeast that has settled out, and even perfectly clear wines where you can't see a flashlight beam through them still have some yeast cells in suspension that could wake up and start munching on the leftover sugars.
Be careful about bottling unstabilized meads and wines, do a forum search for "bottle bomb" and you'll hear some horror stories...
"The main ingredient needed is 'time' followed closely by 'patience'." - The Bishop 2013
"Good grief! If someone wanted to murder you, all they would have to do is ship you a 55 gallon barrel of honey and watch you document working yourself to death!" - Vance G
"When you consider that laziness and procrastination are the fundamentals of great mead, it is a miracle that the mazer cup happens." Medsen Fey, 2014