This statement actually means nothing.

All it means is that kids with wealthy parents go to public schools..... That's it, nothing else.
Fees to send your kid to a public school in Finland and almost anywhere else in the world, costs fuck all.
Meaning that the school doesn't receive any extra funding from the wealthy, as it's the same expenditure across the board for every pupil attending.

And what..... Are you saying there are no private schools in Finland? Do some research, you will find that there is.
The way they are funded however, is not like in America, that's all.