Where this term or misnomer came from is beyond me. A chord is a chord...

From notice:
Most classical music is built on simple chord forms. You don't hear many 9th, 11th, or 13th chords in classical music. The extent of most voicing in classical music are 7th's.

I have no understanding of this statement. Bach is not classical, but baroque. He did lots of 7 and 7ths, 9, 11, and 13s.
I don't get this logic. Bach would have been, probably, as good as Charlie Parker. Bach was great in HIS idiom and time. This word "classical" is simply incorrect. One might would suspect that Charlie Parker and Dizzy listened.