Well, my Duracell Platinum AGM battery lasted almost 5 years. Bought it in May 2016. It tested bad and was bulging -- the guy at NAPA thought it had frozen, which I didn't realize was a thing. Regardless, it was clearly toast.
I imagine most people don't know that. Also the temperature where the electrolyte will freeze is charge dependent. A fully charged battery will have a lower freezing point than one that's discharged.
Have to think back to chemistry. The electrolyte is sulfuric acid, H2SO4, with approximately a specific gravity on the order of 1.1 to 1.4 in batteries. The actual value depends on temperature, concentration (which is a function of battery type, deep cycle are usually higher density) and state of charge.
Anyway, an example of freezing point for battery electrolytes. This isn't universal, the actual chart will be unique for each model of battery, although they will all be similar.
I kind of doubt your battery actually froze since you don't live in the mountains or Wyomikota where you'd see the sustained low temperatures. But if it was old and left substantially discharged it's a possibility.
The cases can bulge just from aging, the hot and cold, UV, ozone, acid just wears them out even without the added pressure of frozen electrolyte. Remember water expands as it freezes and battery acid is roughly 25% to 50% sulfuric acid diluted with water.
There's some connection here to how you pay for a battery and the simple quality of the components they use. Cheap batteries use thin, cheap plastic. That's just economic reality. Then how much air they ship you inside the case factors in. A higher end battery will have more lead and acid and therefore less room for expansion since the outside dimensions of a battery are fixed by BCI specs.
The take-away, keep your batteries charged and you'll probably never freeze one.
