Also, it could have been a red-eye flight, I think there were changes recently that made nuts optional for those flights. But they make it readily available in case someone would ask.

I believe they are all considered short...those would be flights where movie was not offered (prior to the recent changes on CX Studio). Although I may be wrong.

I think you're right :) These 3 routes served what I called a 'lighter' meal. If one notices, they serve everything on one tray at one go (smaller starter plate usually consists of cut fruits or a rather unappetizing starter and the same-sized desserts plate with like chocolate mousse or just Haagan-Dazs ice cream).

Other longer regional routes (SIN, KUL, DPS) serve the full-on meal; crew come collect your starter plate once you finish before presenting you the main. And they would collect your main before the fruits/desserts trolley being rolled out at your seat.

Re: nuts - not sure why the inconsistency. For every J flight I took except HKG-TPE sector, I have been offered proactively.

This is my experience, as observed by most above:

LH: Always offered warmed nuts with pre main meal service drink.
Japan: Always offered the Japanese rice cracker snack mix pre meal service.
SH: Not offered nuts proactively.

Interestingly, though: When on a SH if I indicated that I will not eat to SP/FP/BC, either before hand (when menus are given out) or when the trolly rolls by, I am offered nuts from trolly with my drink.