My teacher told me that Mochizuki used these names for the techniques so he could remember them easily. My personal oppinion is that he did this to separate his style from Ueshiba's.
I read somewhere that when Mochizuki went to France he tested aikijujitsu against savate, boxing, wrestling and fencing. According to him, he found aikjujitsu difficult to use so he changed to judo and kendo winning easily. Upon returning to Japan he suggested to Ueshiba that aikido be altered to suit modern times but Ueshiba wasn't interested. Anyway Mochizuki went on to do his own thing.
You are right about Mochizuki coming from a background of mixed martial arts. Its also possible he took the names from jujitsu and judo.
I only met him once in 1996 in Shizuoka. Interesting person. I wish I had this question on my mind back then.
Ikkyo - Robuse rowing a boat
Nikkyo - Kotekudaki wrist smash
Sankyo - Ikichigai crossing or passing by...
Iriminage - Mukaidoshi facing drop
Hijishime - Hijikudaki elbow smash
Robuse is interesting. The kanji is ˜E•š‚¹. I can't seem to find this combination in my dictionaries.