Come to reddit's /r/cscareerquestions one day. Tons of stressed out 18-22 year olds practicing CTCI and LeetCode for hours just for a chance at passing the Facebook/Google hazing. Because these people are usually "high achievers" who spent hours in high school at SAT preps, this feels natural to them, which is why they'll give questions like this when they hire in the future.
I do have a problem with it when it's for smaller companies that get 0.05% the number of applicants though!
Unless you're interviewing as a Python syntax expert or something like that.
But just that: a little funny. It's certainly not a deal-breaker; we don't expect perfect syntax at all. For all I know you often switch between Python and JS in your day-to-day work and could easily make such a small error in a high pressure situation. That said, I'll notice it and take note. If one of four or five interviewers says "<name> incremented funnily" nobody will care. If every interviewer is saying "<name> doesn't seem very fluent in their chosen language" then the red flags start coming out.
Likewise, I've seen our recruiters shit themselves trying to sell candidates because they had a competing offer from another A-list company. Getting competing offers is excellent leverage to maximize your starting salary / equity.
Ridiculous enough. Then there's the content. The videos are a presentation by Gayle McDowell, the author of Cracking the Coding Interview. Lots of tips about interviewing, 95% of which were pretty obvious but most of which seemed useful enough, on the assumption that the process is a given. But McDowell would repeatedly say things like "most interviewers won't expect you to write perfect syntax on a whiteboard, but some will" as if this was perfectly reasonable. And she gave "if you're writing in Python, it's a red flag if you use ++ (instead of += 1)" as an example of something she cares about herself! So both the recruiter and McDowell recommended doing a number of pen-and-paper practice coding problems before your interview, specifically on the basis that this is something you never do in your day job.
If I want to be charitable, this is Facebook trying to even out some of the biases introduced by their (apparently unchangeable) whiteboard algo puzzle interview questions, by ensuring everyone is prepared.
If I want to be less charitable, the demand for hours and hours of preparation is just (further) hazing to prove dedication.
In either case, I think this evidence that BigCos are not necessarily any more rational about hiring.