The nickname "KETSUNE" expresses the playful mind typical of Osakans.
The original kitsune udon uses Kyoto's abura age (fried tofu), flour from Kumamoto, dried bonito from Yakushima, salt from Noto, kombu (kelp) from Hokkaido, shoyu from Shodoshima, and sugar from Awa - a parade of delicacies.
In 1893, the founder of Senba's Matsubaya Main branch, Usami Yotaro drawing from his past experience working in a sushi shop served abura age on the side.
Apparently, the customer who put the abura age on udon loved it and praised the udon, giving rise to kitsune udon.
The main (and perhaps the only) reason why this kitsune udon was loved by Osakans was because it was indeed, reasonably priced.
This, may be the difference between soba, which has a complicated story and theory behind it.