When I added comment in post. Instead of showing me comment. Stack Overflow generated the index page in comments section. This is not the first time I saw that but I have seen this many times.
Sorry, but there's no way I can see this happening, so I'll have to assume that this is a problem on your end (my first guess would be a horribly broken proxy).
I have checked the logs; your request when posting the comment was recorded by the load balancer to have received a response of 786 bytes in size. That sounds about right for the expected response (the list of then-present comments, which is then inserted in the appropriate place), but is orders of magnitude below the size that a response containing the full home page would have had.
So something between us and your browser replaced the response. Note in particular that this misplaced homepage in your screenshot has a "log in" link. Had your browser requested that page, it would have had your name at the top, since you were logged in.