That description is from a player generated site and thus reflects only the public opinion of the job.

Here's what SE has to say about RDM:

"These fighter-mages can utilize both black and white magic, as well as the arts of the sword."

also

"Capable of using both white and black magic, and adept at swordsmanship.
However, mastering powerful spells takes far longer than white or black mages."

and just in case you need it:

Adept

adjective
1. very skilled; proficient; expert:
"an adept juggler."

noun, adept
2. a skilled or proficient person; expert.