What qualifies as a bestseller?

So, my most recent novel (released on Monday) is currently at #68 in Christian fantasy on Amazon, which I believe is technically a bestseller because it’s in the top 100 of its subcategory. But… I feel a little sleazy saying it’s a bestseller because it's sold relatively few copies (the sales numbers haven’t updated yet, but I’d be shocked if it’s over 100).

Anyway, I did some internet research, and it seems like some authors are totally fine with calling a book a bestseller if it hits that top 100 in their subcategory, and others will only do that if it hits the top 100 overall, and others will only do that if it hits #1 in the subcategory… and I’m desperately confused by it all.

I did find the advice to say that it’s “top 100 bestselling in Christian fantasy on Amazon,” which still has the benefit of saying it’s bestselling while still being honest about the fact that it’s only bestselling because of the highly specific subcategory. That’s currently my favorite of my options (because I am really excited that my marketing actually paid off, at least a little bit, but I still want to be transparent with my readers), but I also wanted to get the input of more experienced authors.