A hot fix is automatically applied at the "Press Start" screen when Borderlands 2 is connected to the internet. In general, hot fixes are used to temporarily address issues between major updates. Hot fixes are not permanent -- they are temporarily stored in memory during the game session and lost upon exiting Borderlands 2. To ensure that you receive hot fixes, make sure that your system is connected to the internet when Borderlands 2 boots up.
I don't think it was due to a hot fix according to this.