They aren't the biggest "record store in the world".
They are a department store.
A record store (A) sells RECORDS (they are still manufactured) and (B) sells primarily music albums and related materials and (C) typically sells albums beyond what is in the Billboard top 20.
Your point is well taken; however, Walmart is the world’s largest seller of prerecorded music. Personally I don’t buy their stuff there because they carry a bunch of crap I would never listen to intentionally (with the possible exception of the last AC/DC disc).
>>RECORDS
As far as I’m concerned a “record” is short for “recording”
and, while people may associate it with 33, 44, or 78 rpm
vinyl, technically a CD, cassette, 8 track, mp3 file, etc is a record. A record-ing.