Could you see signs of fluid leaking out of the strut?
I have heard of situations were, if the strut or shock was leaking, it could allow water to get inside. This water can freeze and cause the strut to seize up.
If this were the case, by letting it set out in the open allowed it to thaw out.
I don't know. That is the only thing I can think of. That is unless you have gremlins around your house or something.
