Each usually takes a singular verb and pronoun.
But sometimes these can be plural, e.g. when you have each of them.
For example, There are about 50 states in the US, and each of them have something beautfiul to see. (You could also say each of them has something beautiful about it.)
If you start a sentence with they, then you would say They each have ...
I wonder if the sentence is using "them" in its modern singular form (where it replaces him/her, when you don't know the gender). Someone who has gotten very used to saying "about them" instead of "about him/her" might go ahead and use it for the neutral gender "about it" without stopping to think.