So, here is my analysis, for what it is worth... for what you are willing to "pay for it" ....    ;)

You think every plant is the same, every plant is identical.  Well, it is not.   My thinking there slight difference at the cellular, in how much "solid goodies" are in each cell vs how much water is in each cell.  The plant cells with less "goodies" in each cell were apt to freeze more quickly; the plants with more "goodies" in each cell had a lower freeze point.  There might be just enough difference that some plants were able to withstand the frost.  

Seems like a logical explanation to me.