A couple people have asked about this, and its useful to know beyond this particular topic.
"The Law" consists of Statuatory law, Rules & Regulations, and Court opinions and precedents.
The legislature writes and passes the statuatory law.
The agencies responsible for carrying them out have to develop the specifics including the procedures for executing them.
Decisions in court can further clarify (or muddy) the interpretations. (This is when lawyers from both sides come in with examples of at some other time/place/situation the same law was applied with the outcome they arguing for.)
This rule and definition change (already summaried and linked to) was ATF's job to come up with, post for comment, etc. because of the Bipartisan Safer Communities Act passed by Congress in June 2022.
S.2938 - Bipartisan Safer Communities Act
If the changes don't seem to align with the Act, then when enforcement begins, the person(s) affected will have grounds to challenge in court.
The same three parts of law come into play when deadly force is used for self defence. IMO for this reason alone, fire arms owners in particular ought to be familiar with this, and the relevant specifics of all three for the locality you are in.