Real pints of 20 Imperial Ozs too

The last time I was in the United States, I went into a bar (on Lower Murphy Avenue in Santa Clara) and asked for "a pint of Sam Adams". I wasn't really paying attention and it was only when the waitress asked if we wanted another round that I noticed that I'd been served a 20oz glass, whereas my colleagues had both been served 16oz glasses. Perhaps my English accent is more convincing than theirs? It was an "Irish" bar, so perhaps they're more attuned to British, as opposed to US, units?

Peter