last winter my 15 gal Angie mango, was left outside unprotected....I got lazy, and laid it down underneath an oak tree.
temps got down to 26.5F briefly...I suppose the mango saw about 27F for 2 hr
it died back and I lost half of the tree, but now about a year later, the tree is really pretty!
for a mango tree to be considered cold tolerant, I'd say it would need to be able to withstand the same treatment, without having any significant damage.
Large mango trees here in central FL easily survive brief dips down to 28F without major damage...and some even survive 25F...but they die back to stumps....and all seem to be in protected locations...(so they probably stay above 25F if that is the air temp)
i wouldn't be surprised if there is a "cold hearty" mango seedling lurking somewhere in FL, but it's probably one out of 100,000 trees...and the fruit taste like Tommy Asskiss!