True, although I wouldn't go so far as to say it is "obsolete." That being said, English is a rather ambiguous language. Obsolete might mean it has nothing of value for the reader, and it also might mean there have been some developments since its publication so be sure to do further reading.

Given that Clojure is not the only Lisp, I feel the article is still relevant although comments like yours and another poster pointing out the value of Clojure add value for readers.