Anything that consists of several interconnected parts that together perform some function can be called a system, and almost every product does consist of several interconnected parts that together perform (or are claimed to perform) some function. Thus, practically anything that is likely to be offered for sale can, so far as semantics is concerned, be called a system; it is not false to call it a system.
On the other hand, so far as pragmatics is concerned, the word system is usually used only when a thing's being a system is somehow noteworthy; it is thus typically used only for relatively complex, ingeniously structured systems. Using that word for something relatively simple is therefore misleading, even though it is not false.
It is not false (although it is misleading) to say that a liquid preparation of vitamins is a system, because it does consist of several ingredients that work together. Alternatively, it can be argued (as has been done by Accumulation) that the regimen of using the preparation is a system.
Advertisers often try to find ways to say things that will mislead the intended audience, without being, strictly speaking, false, so it is not surprising that they make use of the word system to create the impression that their products are more complex than they are, while avoiding the legal troubles that could result from saying something that is outright false.