Programming: what does "to bump a counter" mean?
It means, as you guess, to increment the counter. See also the phrase bump up, which means "to raise". It's not stated how much the counter gets bumped but presumably that's not important or it's 1.
The phrase used in the example is to bump a count and not to bump a counter. It's not a stock phrase but is an idiomatic use of count in the sense of tally and bump in the sense of increase or nudge forward.