The license being charged from every taxpayer and collected using tax collection mechanisms doesn’t make it a tax.
The difference is that a tax would be collected into the budget and SVT would be funded through the budget.
A license on the other hand is paid directly to the public service companies which (in theory) gives some amount of political independence.
So: license, not tax.
It might look to some like a useless distinction “how is money paid on my tax bill not a tax!?”, but there is an important difference.