1/48 scale was used by Aurora way back in the 1960 for their line of tanks and also by Bandai in the 1970s. Back then, most kits were built to box scale and individual companies released kits in their own standard scale.
Revell did armor kits in 1/40 scale.
Renwal did armor kits in 3/8" scale which worked out to 1/32 scale.
Monogram did 1/35 then moved to 1/32.
Tamiya did 1/50 scale then moved to 1/35 and also produced motorized 1/48 scale kits. Their 1/35 scale kits set the standard that became the industry standard.