[Hobohodo]

I think a better fitting analogy for relationships would be: Married people should ensure they have independent friendship circles, hobbies etc. to ensure they don't end up becoming too dependent on each other and unable to function separately.

I'm not sure how well this maps to the article but have heard this advice before. Of course, never having been married I can't speak of its efficacy.

[js8]

What you mention seems more like (also common) advice to keep your skills sharp (for example, have a hobby project on Github in a different programming language) outside your professional job. It is a related but different advice than to go shopping around on job interviews.