Apparently this happened at Johnson Space Center in a vacuum, so the temperature would be high enough to make that happen with the reduced atmospheric pressure (see the chart at [1]). The temperature in space is far, far colder, I don't see how this could happen.
EDIT: According to the replies at [2], the retained heat of ejected astronaut urine is enough to first cause boiling but that heat runs out quickly and you get ice crystals.
Well as far as spit on the tongue goes, any water that doesn't boil off remains in contact with the tongue/cheeks, conduction being way faster that radiation at 37c any spit that did freeze due to evaporative cooling would thaw out again very quickly.
It's different for urine which lacks the continual heat source. If you had a mouthful of water, instead of a thin sheet of spit, you'd likely end up with an ice cube for a while.
[1] http://www.iapws.org/faq1/boil.htm
EDIT: According to the replies at [2], the retained heat of ejected astronaut urine is enough to first cause boiling but that heat runs out quickly and you get ice crystals.
[2] http://www.newton.dep.anl.gov/askasci/gen01/gen01060.htm