that's not true: https://www.snopes.com/fact-check/mcdonalds-100-beef/
It's the same in Europe with many types of olive oil - much of it is grown and extracted in Iberia, but then sent to Italy, etc, for processing, becoming 'Italian' olive oil..
Doesn't bother me though - my favourite olive oil comes from Spain...
The problem is that it isn't true - the 100% British & Irish beef is actually beef from Britain & Ireland. It's a myth that it's the company name.
English & Irish law on the country of origin of products is pretty strong and certinally does not allow processed beef from other countries to be labelled/marketed as British. Also a 5 minute google search shows this is just simply an urban legend.
As you were!