In the Privacy Policy document there is an annotation that says:
I decided against using hypothes.is as the commenting system for my blog, since I don't want my readers to be traceable by a third party I choose on their behalf
Alhtough this annotation is a bit old -from 2016- I understand that Hypothes.is server would in fact get information from these readers through HTTP requests, correct? Such as IP address, browser's agent, etc. I wonder whether this is the traceability the annotator was referring to.
Anyway, I think this wouldn't be much different to how an embedded image hosted elsewhere would be displayed on one such site. And Hypothes.is' Privacy Policy states that
This information is collected in a log file and retained for a limited time