Let's look at the big picture and quit fighting about this.
If you think back just a few years ago, backflow preventers were never installed on automatic fire sprinkler systems. That all changed when the plumbing industry brought forward all of the information necessary to add backflow requirements in the code. Sometimes the requirements were placed in the plumbing code, other times they ended up in the building code. I personally prefer when the backflow requirements appear in the plumbing code.
The normal backflow requirement for an automatic fire sprinkler system is a double check valve assembly. When chemical additives are a part of the sprinkler system, such as anti-freeze, the backflow protection is typically by a reduced pressure principle backflow preventer. Some jurisdictions require a reduced pressure principle backflow preventer for every sprinkler installation. I think that is overkill. A double check valve assembly was designed for sprinkler system backflow protection.