<<Disclaimer: Verify this information before applying it to your situation.>>

The 5% acetic acid refers to the acidity or 'strength' of the vinegar.  Five
percent is the standard and is what most recipes using vinegar are based on.

Pickling vinegar (extra strength) is about 7%.     Acetic acid is present in
all vinegars.

My point is that only those apple cider vinegars that are "pure apple cider
vinegar" can be relied upon to be gf.

Hope that clears up the confusion.

Jessie