The guy telling you that is either A) full of caca, or B) ignorant or C) trying to make a buck off of you by selling you his product. I am not a huge CA finish user, but I do on occasion, and it is a great finish if you can do it right on a consistent basis.
First, there isn't a lacquer on the planet that blocks UV rays UNLESS a UV-blocking additive has been added to it (and some do, but they always hype it up and is very easy to tell by the label). Sherwin Williams "Sherwood Precat Lacquer" is a good example. They use it, and they tell you with a big ol' starburst on the can that say "UV Inhibitor".
Secondly, UV inhibitors are not permanent. Third, UV inhibitors vary in their quality. Fourth, the amount of UV inhibitor added to the lacquer likely varies from "useful" to "useless". Just because they dribble a bit in a vat of lacquer and say "UV inhibitor added" doesn't mean it's worth a flip.
Go ahead and use CA all you want. No, it may not block UV rays, but pens aren't going to sit on a hot tin roof all day either--- there is such a scant amount of UV in indoor lighting that it won't make much of a difference.