That is not the truth. While generally not over 6 feet tall, the Olympic distance runners had a very normal height distribution. One of the shorter, Hillary Bor, is still 5' 7".
http://www.runnersworld.com/sweat-science/the-incredible-shr...
Feyisa Lilesa is 5'9" Galen Rupp is 5'11" Mo Farah is 5'9" Bernard Lagat is 5'8" Matt Centrowitz is 5'9" Paul Chelimo is 5'11" Tamirat Tola is 5'11" Taoufik Makhloufi is 5'9" Nick Willis is 6' Evan Jager is 6'2" Mahiedine Mekhissi-Benabbad is 6'3"
https://en.wikipedia.org/wiki/List_of_average_human_height_w...