Don't get too hung up on it.
Beach cruisers emerged in the mid to late 70s and were mostly stripped down balloon (*x2.125) tire bikes. There were also some factory built ones, some of which looked more like BMX frames, still balloon tired at that time. "Cruiser" sort of evolved to include all those, plus balloon tired bikes that still had fenders and/or other equipment.
I don't think there's a difference between "cruiser" and "balloon tired" other than perhaps middleweights tend to get lumped in with "cruiser" these days and they generally didn't back then. Also "balloon tired" is the term from the time when these bikes were ubiquitous in the USA. The term "cruiser" emerged much later.
You also see things like English 3 speeds, mixtes, and other random lightweights getting called cruisers on craigslist, ebay, etc. Nope.
If someone is talking about balloon tired bikes, it is more likely to mean the 1933-1965 originals with *x2.125 tires that we have a forum section for. It wouldn't have to mean that though. You can go down to Walmart right now with $150 and ride home on a balloon tired bike. Whether it is any good or not is a separate issue.