I get the spirit of the rule - if we're thinking of NCAA and/or NFL; however, the HS rule states (in english) if you're tackled via a grab on the inside back or side collar of the shoulder pads or jersey, it's a horse collar. Period, end of story.
That being said, it seems the spirit of the rule for NFHS is they don't want players to tackle in that manner at all.
Easier call to make with NFHS that if runner is grabbed that way & tackled, it's a flag. No determining whether legs buckled and/or runner fell backwards.