Reminds me of the fight he won his WKA US cruiserweight title. By the time of this fight, Nielsen had already made the transition to muay thai style, but he still fought like his old full-contact karate days. As his former mentor Benny Urquidez said, "the way you train is the way you react."
Indeed! I've heard some people express doubt about Nielsen having studied Muay Thai for this very reason. He did, of course, but the peculiarity is how he applied it. Don's style from the late 80s onward was Muay Thai via America kickboxing, and that looks a lot different than the original.