Because of the bits of sand thrown about by Tṛṇāvarta, people could not see themselves or anyone else, and thus they were illusioned and disturbed.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
नापश्यत्कश्चनात्मानं परं चापि विमोहितः । तृणावर्तनिसृष्टाभिः शर्कराभिरुपद्रुतः
nāpaśyatkaścanātmānaṃ paraṃ cāpi vimohitaḥ | tṛṇāvartanisṛṣṭābhiḥ śarkarābhirupadrutaḥ
SB 10.7.23