I agree with him.
To try something new is worth doing.
Like him you may find some different or more profound aspect of TKD.
Unlike him you may find another martial arts more interesting or more worthy.
Any case can be good for you.
I also tried some different martial arts like Judo, Hapkido or Jujitzu.
I tried them to support my TKD with enlarged knowledge, and in effect I came to be able to agree with him more.
I also teach another martial arts to my students of TKD department of a University in Korea. They will be masters and they are good at TKD, but I believe it is problematic that many of them know almost nothing of another martial arts.
Even though you were not a master it would be worthy of you to try something new as suggested above.