Legend has it that when the Russian Cossacks occupied Paris in 1815, they were notoriously rude.
They demanded quick service from local restaurants and bars by shouting what the French understood to be “Bistro!” which sounds very much like a Russian word for “quickly.”
The word bistro has no French root, and so the legend is plausible.
Regardless, whether French or otherwise, a bistro promises intimate and rapid service.