Not necessarily.
For items like CRTs the companies often contract out the actual manufacturing of the product. In other words they just sell their name so the other company can put it on. In this case, yes, Philips owns Magnavox, and they just opted to use that particular brand on the CRT.
For example, Toshiba CRT TVs are actually made by Orion (a really crappy TV manufacturer). Of course I learned this AFTER buying a Toshiba TV :/