This game has crap hit registration and a big shot delay so if you flick shot it was probably due to your reticle being center at trigger pull but high and right or left at the time of the bullets actually firing. I'd say it's between .2s and .5s from trigger pull to your bullets actually shooting...
Could be lag, could be glitchy hit box, could be a lag swag user.
Without any context or video, all we can do is list could be's. Which in this game, there is a lot of could be's.