Those actually are double the normal resolution... Hard to compare it to xenforo.com since they use different icons, but they actually are retina.. Check the RSS feed icon here vs the one on my site as an example.Nice. I didn't look at avatars. Well done
Forum icons though aren't done. See folder icons and forum selection icon on screenshots below.
The icons aren't full vector (SVG), but they are double the resolution (well really 4x since it's double on both x and y).