The modified BIOSes over at TweakTown are not official Gigabyte BIOS versions but have been amended by end users to include features, some of which are newer, which are not yet available in the official BIOS releases and which may not be included in their entirety by Gigabyte when a newer official update is released.
In the case of the modded BIOS for your motherboard it includes newer versions of the Intel Rapid Storage Technology - 11.6.0.1702 , Realtek - 2.50 and JMicron - 1.07.28 than are used in the official F13 BIOS.
Using a modified BIOS is done so at your own risk and will usually void your warranty if you need to RMA the motherboard, so the use of these modded BIOSes is not recommended for the average user.