alt Hacker News> but that's not the answer we wanted
You could have learned this if you were better about collecting requirements. You can tell the interviewer "I'd do it like this for this size data, but I'd do it like this for 100x data. Which size should I design this for?" If they're looking for one direction and you ask which one, interviewers will tell you.
I've done that too and, in my experience, people that ask a scaling question that fits on a single machine don't have the capacity to have that nuanced conversation. I usually try to help the interviewer adjust the scale to something that actually requires many machines, but they usually don't get it.
Said another way, how do you have a meaningful conversation about scaling with a person who thinks their application is huge, but in reality only requires a tiny fraction of a single machine? Sometimes, there's such a massive gulf between perception and reality that the only thing to do is chuckle and move on.