True, I just think it's a bit crazy. I couldn't imagine a modern person in Austria thinking that anyone from Serbia was essentially Austrian. I definitely couldn't imagine them believing that "the Serbs just want to be Austrian anyway"...
Regardless if a British person claims Irish people as being British then they should also be claiming people from the US, half the Carribbean, Sudan, Lesotho, Benin, Kenya, Nigeria, Ghana, Somalia, Nigeria, Zambia, Malawi, South Africa, Saudi Arabia, Qatar, Oman, Bahrain, Iraq, Kuwait etc etc.
It's ludicrous and shows a complete ignorance to history, but then again a lot of my mates from the UK do say that very little of this is taught in schools - specifically the history between Ireland and the British Empire.