Surely you are not processing data in this case though? The client (software) determines whether to make a connection to fonts.google.com. Your website never passed the information to google.
The user likely has no idea they contacted Google — it only happened because the code in your application executed it.
The reasoning was that as it is so very easy to self host Google fonts and with caching as an argument gone there is actually not enough reason anymore to use the hosted version by Google and transmit PD to Google.
Would the site have used a foundry that didn't offer self hosting the reasoning might have turned out differently if the site owner could have made a strong argument for using this specific font by this foundry.
At least that was my reading but IANAL.
Your website is malware that contains code which makes the visitor's browser connect to Google's server.
Though it arguably doesn't get enforced anyways, except for some big corps.
It doesn't often really work out that way.
Tax Law is especially interesting here, because you can basically depend on what the IRS has said but there's a chance that even if they said X, the tax court will actually rule Y (in your favor). Sometimes the risk can be worth it (if you made a good-faith effort to comply with a reasonable understanding of the law, and the court rules against you, you just have to pay the tax; even if you were found unreasonable you pay the tax + penalty which often isn't that much).