Basically, priests use a prayer book (I believe it’s called the “Sacramentary” but I could be wrong) that lays out the Mass. Words to the prayers are in black, e.g. “The Lord be with you.” The actions they are supposed to take are in red, e.g. bow, elevate the host, make the sign of the cross, etc. Hence the expression.
Some priests have the annoying habit of improvising parts or all of the prayers to fit a given situation or just because they want to improvise.
Okay, now I get it.
My experience (yuk) attending Mass being said by one of these adlibbing showboats tells me that he just wants to call attention to himself rather than to Our Savior.
Kudos to the bishop and good riddance to the showboat.
Deus vult!