Good bet Waymo's software wouldn't do this since it relies on Google's mapping. I suspect any speed sign listed faster than their database contains would be rejected.
FTA: "A group of hackers has managed to trick Teslas first-generation Autopilot..."
Are they still using the "first generation" or is there now a second or third generation of software? If yes, then I'm assuming they couldn't get the hack to work on the newer stuff (or they didn't test it for some odd reason). So, as usual, keep your software updated and you'll be much safer from vulnerabilities.
Regardless, it gives the fuddy-duddies and troglodytes plenty to point at and bitch about.