An issue tracker is a tracker for issues, not the guestbook to the project. You could've emailed the author, link to him on social media, on your website, submit to reddit etc... but you choose to open an issue on his issue tracker, and put that here on HN in a comment. Even if you intended differently, it's how it look to an outsider.
On your last paragraph, yes, github used to show who reports issues as contributed to the project to which they reported. I recall at one point having reported an embarassing silly issue (a very stupid config mistake I made that I don't recall) to Pelican blogware and it went there among the contributed projects as a badge of dishonour. :) But now I checked, that section seems to be gone from the profile page on gihtub.
I don't have social media, and GitHub issues are indeed acceptable for giving public feedback of any sort, though I understand not all projects are ran this way. I clarified this point:
On your last paragraph, yes, github used to show who reports issues as contributed to the project to which they reported. I recall at one point having reported an embarassing silly issue (a very stupid config mistake I made that I don't recall) to Pelican blogware and it went there among the contributed projects as a badge of dishonour. :) But now I checked, that section seems to be gone from the profile page on gihtub.