I've been around Americans a long time. 1994 I first got online and back then there were next to no Brits online so I made friends with Americans, many of whom are still friends today. When I landed on the fair land that is the States we and our hosts constantly jibed each other about the need for an English/American translation dictionary :P I offered to write one.. I could be rich if I did!
SO biscuit and cookies... to us they are two different sizes and textures of biscuit..
Anyway... just while browsing idly I saw this article - it's fairly light-hearted :)
https://blog.oxforddictionaries.com/2014/05/biscuit-vs-cookie/
and this.. which ahem agrees with Brits on the matter
https://www.bbcamerica.com/anglophenia/2014/10/biscuits-different-britain
One thing though... can you even imagine the cookie monster getting anywhere in life if he were called the biscuit monster??? Unthinkable!
Disclaimer please dont get mad.. this is meant to be a funny look at language differences