LOL - I can just imagine the mental picture that made for you! The closest I can come is the moment my fiance used the phrase "eat tea". I'm pretty sure something snapped in my brain trying to work that one out! (and I'm sorry for repeating this story from another post - I just hope it isn't in this thread!
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I always thought the biscuits in 'tea and biscuits' referred to the scones and not the cookies, because scones look like biscuits to me (as you pointed out yourself). I can't remember when I was corrected on this subject, but I'm still confused about the difference between biscuit cookies and cookie cookies. 
The only cookies I ever knew that were called cookies in Britain were the Maryland Chocolate Chip variety. Generally there's no difference I suppose. I was trying to explain this to my wife's boss recently and he just couldn't get his head around it. (He's in his 70s, lived in Texas all his life and never been out of the country except over the border to Mexico) and I was telling him that, generally, UK biscuits can be savoury as well as sweet where cookies can't be anything but sweet really. I've seen people spread butter on a digestive and also serve them with cheese.
Personally, I prefer Digestives just for dunking with tea.
Haha! Don't ask me to explain how we know the difference between drinking tea and eating tea. I suppose it's all in the context.
If someone asked me what I was going to have for tea tonight, I wouldn't say "English Breakfast or Earl Grey, Haven't decided!" for fear of looking like a smart ars*!
It's generally a regional thing in Britain I think. For example, I lived in South Devon and I rarely heard "I'm going home for my tea now", "What you having for tea?", etc.. but when I lived in South Wales, everybody used it frequently to describe supper time.