It is a valid convention, but not the only one, and might confuse beginners who will probably be used to seeing library() used in reliable sources. I think library() can be a valid choice, e.g. an analysis script with extensive use of dplyr, or for ggplot2 functions.
There is a later section "Examples why you should avoid library() calls". Again, my preference would be to soften this - "you should avoid" is too strong for me.