Taghlib is not confined to grammatical gender. Sometimes the semantic addressee governs the expression even where a surface noun would normally suggest a third-person form.
«بَلْ أَنْتُمْ قَوْمٌ تَجْهَلُونَ»
Rather, you are a people who behave ignorantly.
Qawm is an overt noun that could suggest third-person reference on a strictly formal analysis. But tajhalun directly addresses the listeners: the qawm are those very people being spoken to.