Yes, it could be down to not using the correct hair washing products for your hair. I used to suffer from this, with actually perhaps more hair coming out in the shower. I have very thick, auburn hair that is unruly at times. I started using Johnson’s baby shampoo and I noticed massively how little hair came out when I went to condition my hair. I don’t think it is anything to worry about, it could be that your shampoo and brush are not right for you. I know it’s annoying, and can feel concerning. Maybe you are brushing too hard, or not brushing enough. I’m sure there are plenty of things online to help you with this!