Ramban: He meant either that the episode with the rock, which ended with his being punished, was the result of their quarrels (with Hakadosh-Baruch-Hu) or that he needed to strike the rock twice (not in accordance with Hashem's instructions ¹ ) due to Yisrael's doubts. ²

Seforno: He meant that his punishment not to enter Eretz Yisrael (which they caused) was meted out to him in order to facilitate sending their children into Galus ³ and shed genuine tears annually - to bear the full brunt of the sin of the Meraglim. ⁴ And this would have been less severe had Moshe entered the Land together with them. ⁵

Da'as Zekenim and Hadar Zekenim, ⁶ : When we said 'Shall we take water for you from the rock', you thought that we [said this incredulously, for I] thought that water will not emerge. However we should have explained that Hashem commanded me to say that. And Hashem was angry with me - because of you.

Oznayim la'Torah: 1:13:5:1. He therefore pointed out that, in his capacity as the leader who had erred by agreeing to send the spies, he was being punished on account of their sins. ⁷

Ramban #1: He was reprimanding them for causing not only the barring of their entry into Eretz Yisrael, but also his. And he was making a point here of mentioning the punishment of all those who were barred from entering the Land.

Ramban #2: He did so in order to mention Yehoshua ¹ who would replace him as the new leader and who would take Yisrael into Eretz Yisrael, since he was being punished by means of a decree forbidding him to cross the Yarden.

Seforno: Refer to 1:37:1:2.