It's quite simple. All versions that are not coming from Thunderdark are derivative versions of the mod. That's true for Cal's UE version of MFFS and for our classic version of the mod. Now I'd prefer to stop discussing this topic and focus on the next steps in bringing you a stable release of MFFS classic.
You have to wait for IC² to stabilize before.
Currently there are 4 MFFS versions :
Thunderdark MFFS (father of other three MFFS "versions" , discontinued as he stopped modding)
Immibis MFFS (First child, when thunderdark switched to modular items instead of modular blocks)
Calclavia MFFS (Second child, when thunderdark stopped modding and gave calclavia the rights to make his own MFFS, which got modified to an UE addon instead)
Minalien and Searge MFFS (Third child, when thunderdark gave minalien permission to continue his mod, keeping it an IC² addon)