I guess we need some Welding 101 here (I have been doing arc welding for many, many years)
Oxy/Acetylene:Flame is heat source for welding process.
Filler Metal is added manually by hand.
Shielding Gas is the CO2 produced by the flame.
TIG = Tungsten Inert Gas:Utilizes the arc between the base metal and a tungsten electrode as the heat source.
Filler Metal is added manually by hand.
Shielding Gas is used.
(similar to Oxy/Acetylene but arc is heat source and gas is added)
MIG = Metal Inert Gas:Filler Metal provides arc heat for welding process.
Filler Metal is on spool with auto feed.
Shielding Gas is used.
Flux Core:Filler Metal provides arc heat for welding process.
Filler Metal is on spool with auto feed.
Filler Metal is hollow and filled with welding flux which burns and the gasses produced act as the shielding gas.
(flux may include other chemicals & metals to form an alloy as base metal and welding wire mix)
So while Flux Core may appear to be like MIG, the processes are distinctly different.
Of course then there is the wire/flux selection to match the qualitites of 4130...