Commentary for Numbers 11:7

והמן כזרע נד AND THE MANNA WAS AS CORIANDER SEED — He who said that (the previous verse) did not say this: Israel said, “our eyes are only on this manna”, but the Holy One, blessed be He had it written in the Torah, and the manna was like coriander seed” — as much as to say “See, ye people of the world, about what My sons were complaining, whilst as a matter of fact the manna is excellent in so many different ways!” (Sifrei Bamidbar 88).

והמן כזרע גד הוא, whereas its appearance was like that of crystals. In other words, whereas in fact it was soft inside, it appeared hard from the outside. When looking at it the people said ונפשנו יבשה, “we are completely dried out, like someone who has to eat hard and dry kernels of wheat. If so, why did G’d become angry as we are told in verse 10?
Now the Torah explains the reason for G’d’s anger. When the people would grind the manna crystals in their mortars or mills, its taste was like something creamy, oily. This taste which originally had been described as similar to crackers smeared with honey (Exodus 15,31) changed to be like nuts after they are ground. After undergoing grinding it now became moist and like an oily substance. Seeing that it did not taste dry at all, the people’s complaint was unfounded, and this is why G’d became angry at the unjustified accusation that the manna was the reason that their whole system dried out. In Beshalach, where the taste is described as a wafer smeared with honey, the Torah spoke about what the manna tasted like raw, in its original state, prior to assuming the taste of rich cream.

Round. Rashi is answering the question: The manna was white, while coriander is black, therefore why did the Torah say that it was like coriander seed? Rather [it was shaped like coriander].