Although the Kumaras were right in such acts of refusal (refusal to generate progeny, in order to aim at liberation), Brahma, being absorbed in the mode of passion, could not check his passionate anger
SB Canto 3
On the refusal of the sons to obey the order of their father, there was much anger generated in the mind of Brahmā, which he tried to control and not express.
Brahmā is the director in charge of the mode of passion of material nature. Therefore it was natural for him to become angry on the refusal of his sons to obey his order. Although the Kumāras were right in such acts of refusal, Brahmā, being absorbed in the mode of passion, could not check his passionate anger. He did not express it, however, because he knew that his sons were far enlightened in spiritual advancement and thus he should not express his anger before them.