It not really all that odd in retail. “BOGO” (pronounced bo-go) is quick to say on the floor and is less awkward than “BOGOF” which sounds like either a franken-portmanteau of “beef” and “stroganof [sic]” or an amateur spy’s attempt at a cover identity.
It’s also used more generally for buy one get one X% off sales and you’ll see lots of “BOGO50” promo/coupon codes. Then marketing jumped on the bandwagon and started plastering “BOGO” all over marketing material so consumers are used to the lingo now