The reason why it took so long: The card machine to pay the tax was broken. Banks were closed, ATM limits too low, so he had to wait for a replacement card reader to arrive.
It's unclear if he actually failed to declare it or if there was some other kind of mistake. It's also unclear if he had to pay a penalty or just the tax.
However, a source told CBS News, the BBC's US partner, that Schwarzenegger was not asked to fill out a declaration form.
So yeah, the headline and article are making a big thing out of no information.