> no matter how small a component already is, the single-responsibility principle can still be applied: every line of code can be assigned its own responsibility

The definition of SRP is to have each class (or module) to have a single reason to change. I don't see how that has anything to do with having each line be assigned a responsibility. If the line changes for the same reasons as it surrounding lines, then, they are part of the same component (to use the author's wording). My guess is that the principle is being taken literally from its name/acronym.