That thing of beauty is nothing but wrong. It was an unfortunate try of looking smart. According to ou dictionary ethnicity means a group if people with a different culture (creed, political view, different language and different race). By our standards, for example, white british are not an ethnic group, but black british are an ethnic group because they are derived from Africa, which holds several different ethnicities opposed to ours. I know that this might actually soud strange, but in fact it is real. So the answer of the other guy is an hollow, ignorant argument.
I consider 'ethnicity' to be defined by race, genetics, ancestry etc.,
I consider 'culture' to be defined by language, customs, ideologies, ways of doing things, values, concepts & traditions held dear etc. I consider 'nationality' to be defined by what your passport says and where you live.
For example: While a 5th generation NYer name Joseph, born & raised in NYC, whose great, great grandparents emigrated to America from Italy, may share a common ethnicity to a guy named Giuseppe who has lived on a vineyard in Tuscancy his whole life, they do not share the same culture. At some point however, they may share the same nationality.
North America is different from Europe, because it's population is derived mostly from emigrés as opposed to the natural geometric population increases that we see in older countries and cultures. While North American population increases were caused by a different set of factors, This uniqueness imo, reflects the often overlooked fact that ethnicity & culture are not necessarily the same, and that unlike Europe, one's ethnicity is not necessarily an accurate barometre of their culture. The very difference between Canada & the USA punctuate this point precisely. For all our similarities, we are two very different people.