Question about fq_collisions

Hello,

On the 2.4ghz radio,when checking the stats of the aqm file in /sys/kernel/debug/ieee80211/phy0 I can see:

fq_collisions 15709

By comparison, the 5ghz radio has 0 collisions

My question is: Are those collisions inside the fq algorithm, or they are collisions between the wifi frames over the air?

Thank you, happy holidays.