The Brenneke was first. Not sure but the Brenneke keyed on heavier bullets. I guess Winchester wanted something that kicked less than the 30/06,and shot fast/flat. I don't know why .277 but have read reasons.
Anyway the 270 is a true 7mm. It was also an American cartridge chambered in an American bolt action and shot American ammo sold by Winchester. At the time it was among the fastest factory bolt action cartridges you could buy. That's a big deal in 1925.
