I just caught that on a video tape about R/C airplanes, from a guy who really knows his stuff.
I worked in electronics for several years, and everything was done with an iron, not the gun.
Electronic circuits are very sensitive, but we overlook that since they are usually very stable.
In any TV, VCR or other circuit boards, certain components are shielded to protect those components from electrical, radio or magnetic interference.
There is no shielding in a Rx, and the transformer in a Weller or other 'instant on' gun gives off a strong magnetic field. It's one of those things you might or might not get away with, but once I know it's a potential problem, I won't do it for any reason.