To be fair, I've stored people in my contacts like this if I did not know their last name. Dan Bugguy, wherever you are, hope life's been treating you well.
That's also the exact way surnames first appeared and evolved, as well. Which goes back a loooong way. Even the Romans with three names usually had one (the last) as a descriptor of sorts.
Correct. The first "John Fletcher" would have actually been a fletcher. And then he may have named his son "Paul John's son", shortening to "Paul Johnson".