beitza 2b - manna on Y'T

I heard the following from Rav Yonasan Sacks shlit"a:
Tosafos quotes two opinions as to whether the manna fell on Yom Tov. The gemara Shabbos 117b relates the obligation to eat three meals to the passuk of "achluhu hayom" while the gemara Pesachim 105a relates that there is an element of kavod shabbos in the seudos (kavod yom adif m'kavod laylah - see also Gittin 38b). Based on the gemara about kavod there only seems to be a requirement for two meals (kavod yom and kavod laylah). Apparently there are two chiyuvim in seudos shabbos ("Ichluhu hayom" and kavod/oneg shabbos) The third meal is only a din in "ichluhu hayom" and not in kavod (this is evidenced in the fact that S"A 291:3 allows splitting a daytime meal to fulfill seudah shelishis, which obviously involves no enhancement of the oneg/kavod hayom.)
The mitzva of kavod/oneg relates to Y"T (see Rambam Y"T 6:16) but if the manna did fall on Y"T there is no mitvah of "ichluhu hayom" and thus no mitzvah of seudah shelishis. If the manna didn't fall on Y"T there is a mitzvah of both (just like by shabbos).