Yes, it means that if you want to use that function coming from the Rcmdr package then you should do it explicitely, like Rcmdr::errorCondition(). For that function it is probably irrelevant but functions like select() are often masked by several packages.

For example, the tidyverse has dplyr::select() which is often masked by the AnnotationDbi packages, so I always do dplyr::select() to avoid any conflicts. Same with functions such as cpm() which are used by packages in the single-cell world and something like edgeR.