The license fee is a mandatory tax on all television ownership, regardless of whether you watch the BBC or not, whose amount and rules are set entirely by the government. When thinking about how much financial independence the BBC has, you can more or less just think of it as government funding. Also, the BBC World Service (which broadcasts news to the rest of the world) is partially funded by direct government payments as a form of "soft power" influence and used to be even more dependent on direct government funding.
It’s not a tax, as it isn’t collected by government. It’s also not ‘on all television ownership’ - you only need to pay the license fee if you watch public broadcast television as it airs, or you use the BBC iPlayer.