'Normalcy' is not a British English word. 'Normality' would have been my chosen word. Was it written by a US journalist working for the BBC?

Because the journalist in question is aware of some Britishisms, but not others? And it’s not a spelling difference, it’s a different word.

Really? What do you think ‘somber’ means, Ali?

You misunderstood: sombre and somber are the same word with different (British v. US) spellings. Normalcy and normality might have the same meaning, but they are not the same word.

My point was that whoever wrote the piece, if they are American, may be aware of the British spelling of certain words, but not so au fait with vocabulary usage/preferences. Does this make sense now?

One might ask this question:  Is it likely the intent of the original statement would be understood  by a speaker of British English and a speaker of Americanized English?

I would opine yes.  Context adds a great deal to likely interpretations of individual words.  Methinks this to be a tempest in a teapot.

Actually there is very little need for the words "normalcy", "normality" and "normalness". They can always be replaced with minor rewording with "normal" or "the norm".

could easily be replaced with "The day was extraordinarily normal, given..."

It's true that 99% of the time the intended meaning of badly worded and ungrammatical sentences is readily understood, but that is not really a good excuse for institutions such as the BBC!

Even the common (in the USA) expression "I could care less" is generally understood to mean the exact opposite!

What isn’t what? BrE vs AmE spellings are indeed different to (or as I would more usually say, different from*) choice of vocabulary. However, maneuver and manoeuvre mean the same thing; likewise, normalcy and normality mean the same thing; the biggest potential for misunderstandings is where the “same” word means different things depending on whether you’re a BrE speaker or an AmE speaker, the word “pavement” being a popular example.**

“Bonnet” in the context of cars is peculiarly British. When was the last time you heard someone refer to the inner workings of something as anything other than “under the hood”?

________
*In AmE it’s (typically?) “different than”. In BrE it’s “different from” or “different to”; my preference for the “from” variant stems from the fact that you can say “X differs from Y” but you can’t say “X differs to Y”.
**BrE “pavement” is equivalent to AmE “sidewalk”. The word “pavement” also exists in AmE, but with the potentially dangerous difference that it’s equivalent to the BrE word “carriageway”, which is where the moving cars are.