Yeah, I genuinely don't understand what they're going for here. Anything that happens client-side can be modified by the client. Because, you know... it's on their side. Front-end validation and stuff is nice for UI/UX, but nothing that comes from the client should ever be trusted just because you put an obfuscated property on an input or something.
At the end of the day, it all has to be valid HTML tags and javascript that runs without crashing. In terms of security, nothing on the front end even registers on the scale. Absolute worst case scenario, it's like solving a Wheel Of Fortune where I have most but not all of the the letters.
I'm pretty uncomfortable with the description of a user on their own machine, running their own browser running plugins they chose and installed as a "third party" that's engaging in "tampering."