I don't think it's a great question, partially because there are a lot of meta tags there and it feels a bit redundant and slow, and partially because the phrase "first ten lines of Twitter's source code" makes me since - but, I don't see the problem with it. It's a basic question asking you to talk through some stuff. Test of knowledge and communication. There is a right and wrong way to evaluate to evaluate this kind of thing - e.g. "Didn't know about the direction property in the HTML node? Terrible, get out." Would be a pretty lousy interview, but there's no reason to assume the interviewer is going to do that and anyone could beat jerk with any set of interview questions.
I would think that if you would walk out of an interview if the interviewer asked you basic questions then those questions have done their job.
These conversational questions where you talk out some code are probably the most pleasant interviews.
It’s not a quiz, if done right. But you can get to know a lot about someone even by how they respond to not knowing the answer.
Someone with experience knows it’s not a big deal to not know every bit of trivia, but they can talk intelligently about what the code might do. And they know how to find out.
For example, they may point out they know about charset=utf8 in the Content-Type header and admit they thought the meta tag was redundant, and you can have a conversation from there. Or how about "I know 'ltr' means left to right but I never thought about using it with lang=en, but now I want to see what 'rtl' does with English". I suppose it's not the best starter question, but I don't think it needs to be to suss out good candidates from bad ones.
Rage-quitting the interview or blurting out confidently wrong guesses, on the other hand, are bad signals.
I assume that I'm bad at interviews, but I've had people intelligently talk about code, but then completely fail at simple coding tasks. In pretty much all of the cases, they completely understood what was going on, but they were part of a team where someone else was actually implementing it all. So, I think more is needed. This seems to be great for screening though, since it can be done casually, on the phone or while eating a sandwich.
I would think that if you would walk out of an interview if the interviewer asked you basic questions then those questions have done their job.