Earlier quoted context omitted.
It's not the "modern expert system", unless you're throwing away the existing definition of "expert system" entirely, and re-using the term-of-art to mean "system that has something to do with experts".
I don't know what the parent was referring to, but IMO "expert system" is one of the more accurate and insightful ways of describing LLMs. An expert system is generically a system of declarative rules, capturing an expert's knowledge, that can be used to solve problems. Traditionally expert systems are symbolic systems, representing the rules in a language such as Prolog, with these rules having been laboriously hand…
Expert systems are a specific kind of thing (see https://en.wikipedia.org/wiki/Expert_system#Software_archite...): any definition you've read is a description. If the definition includes GPT models, the definition is imprecise.