It's a great first choice, but Javascript on the server is extremely rare, despite the popularity of some very useful frameworks. Anyone giving advice to someone who is quitting a job and learning programming certainly isn't suggesting server-side JS and if they are they are almost certain to be explicit about it, since few resources will mention it.

I think this persons advice will lead them immediately into a point of confusion as they will think that Ruby/Python are actual alternatives to JS. So if this person has some frustrations with JS are they then going to say, well I guess I'll try to get Ruby working in the client... hmm... Ruby in the client doesn't seem to work here. That guy said that Ruby isn't supported on as many platforms so maybe if I change browsers/OS I can get it to work. Hmmm... that doesn't work either. Oh, it turns out that canonically they're used for completely different things!