Not being a US citizen* means I cannot vote in US elections, thus it is a closed door vote by your reckoning and so the US is not democratic. Did I get that right?
*This is shorthand for me not being associated with the US in any way, but you are of course free to reply with all the edge cases that makes the point impossible to state briefly.
He did attack the argument - he argued reductio ad absurdum that classifying "democratic" as "open to everyone" wouldn't be a sensible definition, because the argument would set such a high bar for democracy that no state is democratic.
The irony of this comment is that leaning back and snarkily accusing someone of "playing internet" is precisely the kind of disengagement you're complaining about.
*This is shorthand for me not being associated with the US in any way, but you are of course free to reply with all the edge cases that makes the point impossible to state briefly.