I think what he is saying is since there is a network delay of 300ms for every request, it's better for him to make a single request for a large file than to have to make 10 requests for 200k files and wait 300ms * 10.
This isn't really a problem unique to high latency either, if you have a patchy connection in transit or for some other reason, the UI will suffer.
That just sounds like bad front end coding. A good framework used properly would not have that issue.