A static analysis report of published codebases regarding metrics like line length per function would be interesting to see.
Guidelines should come with a rationale so that in the very least following them when it contravenes their intent can be justifiably avoided.
If I can't understand and appreciate the rationality behind a guideline and I'm not required by coding standards or tooling to follow it, I'm not going to.
Here's a guideline; don't surrender your common sense and let someone's generalized ideology dictate the design of your program.
While I see advantages to minimizing the length of functions, I can't imagine a well written program following this five line rule.
My concerns are that it increases the length of the source code which damages readability, that it scatters functionality and obscures control flow, and that it unnecessarily requires the formation of many interfaces.
The rule is far too general in it's application "all functions" and at the same time too specific "5" to be useful.
If you said instead "in general, try to make your functions do one thing well and divide and conquer the problems until each function is not very hard for you or someone else to understand",
Then OK.