Under that definition, this would be a legal holster:
Remember, that "Shoulder or belt holster" language was copied form the Oklahoma OC law, and the purpose of it was they didn't want someone carrying a handgun in their hand and calling it open carry, and I understand that concern. So they required it to be carried in a holster, and decided to enumerate holster types. Just plain "Must be carried in a holster." would handle this issue without causing any additional confusion.