[minimaxir]

It was my interpretation of the original article quote that it was referring to tidy schema, but I could be incorrect. (the gather() function of tidyr names its parameters key and value as well, and the function is described as "Gather columns into key-value pairs": http://tidyr.tidyverse.org/reference/gather.html)

[ejstronge]

If you are interested in this topic and haven't seen Advanced R, I'd recommend taking a look - the book explains why those functions have key-value pairs as parameter names. Note that the functions you cite aren't related to factors.