Not sure about Czech bottoms but a recent train trip sitting next to a substantial visitor from overseas, they had a backside that amply filled two seats.....
There is also an old Celtic proverb that roughly translated says "if you sit on the same chair too long you'll get hemorrhoids"....
Sorry you had such a bad experience, over here in a lot of subjects and especially sports and music etc. you are often encouraged as far as you can to have a broader outlook rather than tunnel vision. Speaking personally, I found that being a choral conductor taught me so much about phrases breathing on the organ; playing the drums helped with rhythm and coordination on keyboard instruments, and the fingering for early harpsichord music has been invaluable for learning a button keyboard. I'm now learning the tin whistle which really teaches you natural phrasing and ornaments.
I'm sure your teacher meant well, but its like a language teacher just telling a student to learn one language: bunkum because languages all interlace and support each other, much like the way one sort of music making can inform another.