If the bike in question has 16" top tube it will almost definitely be a mini (or variation such as micro-mini or midi)
I think the confusion is that in BMX generally there is no such things as a 'mini-cruiser'...
If it's an OS mini or micro-mini it will definitely be 20" wheels. [obviously pit bikes are 16"]
BMX cruisers are generally 24" [very occasionally 22 or 26"]
Small cruisers are called 'junior cruisers' and also have 24" wheels but would usually be 1+3/8" or 1.5" rims
OS mini = 20"
OS cruiser = 24"