Sounds like maybe they defrosted, spoiled & were refrozen? Rats (or mice) do not simply "explode frozen blood" while in the "freezer" (assuming it's cold enough).
And certainly not in 2 months time being frozen. For the sake of your own health, you might check how cold your freezer & fridge are, so food isn't spoiling. It's also
possible that you had a power outage while away for a while. There's ways to test that.