Correct: all those rock subgenres from a certain era got lumped together as 'rock circa this era.' Things not resembling rock from that era do not qualify. Including things from that era, not resembling rock.

The label having a synonym for old is not carte blanche to slap it on whatever is old, now. By the 80s-90s, classic rock still did not include disco. Or country. Or spacey electronic nonsense. And it never should. Time paved over the fuzzy distinction between early heavy metal and rock & roll, but even that enlumpening didn't just shove both under an existing label. At some point, the term "classic rock" was new.

Calling Linkin Park classic rock is like insisting Imagine Dragons is nu-metal... because it's new, and metal. It's wrong on three counts.