The information will certainly be used for that, but it's unlikely that is the main reason that the gun control side pressured the IOS into creating these categories. It's probably more central to their aims (and more dangerous to liberty) as an exetsion of the Obama era "Operation Chokepoint", which attempted to deny financial services to a range of businesses that the regime didn't like.
Having this show up on payment transactions is going to make it trivially easy for payment processors to drop vendors, for gun shops to lose their bank accounts, for on-line sales processing services to deny access, and on and on. It's just a death by a thousand cuts, progressivily increasing costs and "friction", with the goal of slowly strangling the lawful commerce in arms, as it now appears they will not be able to legislate gun bans.
Yes, I agree with you thoughts there.