What part of GP's one-sentence explanation is not strictly logical? Does obfuscating a simple logical concept by describing it in academia-wanky-terms like Liskov's Substitution Principle make it More Logical? Or does it just make the author and their in-crowd feel more intelligent?

Note, also, that the article isn't even objective. It asserts that the definition of a subtype is Liskov's principle. However, Liskov's principle is only one of multiple possible definitions. In other words, the article is really only invoking Liskov's name as an appeal to authority. So much for strict logic.