It looks like they’re making a separate call for each user avatar in the comments, for example.
The browser does that. How would you expect to get the images except for one by one? It has always been the case for as long as images have been supported.
There is a technique where you put all the images side by side in one file and then reposition it in the view port to show different images. Usually this is for icons since profile pics change too often and would need rebuilt server side each time.
Then you can put all possible images anyone could ever upload as a profile pic into a meta image and assign a 3 MB identifier to each user to specify which subsection of the image to view for that user