Not that far off from mine! Interestingly, my Sync used almost as much as Meet (which I use daily for video calls).
I suspect it's mainly multimedia data, like high-res images. Maybe Lemmy serves higher-res images compared to Reddit? I also recall seeing some discussion somewhere were Lemmy instance admins were turning off server-side image/thumbnail caching, so as a result you could be directly pulling the high-res images by simply scroll thru your feed? This is just a guess though.
Indeed, I read a lot. :) But in addition to manga, I also read a lot of manhua/manhwa, which take up a lot more bandwidth than manga since they're colored.
My guess: Reddit was serving not high res pictures (thumbnails) while scrolling and only gave them when opening.
Instances would need to create a thumbnail and the actual video. This would require a smal-ish CDN and processing power + storage to save the multiple versions to, right?
Idk about NSFW but arent they just hidden? To my knowledge at least Sync only shows "NSFW" and a blank single-colored post for an NSFW post.
I'm thinking similar. I have preloading hires images off and gifs set to WiFi only, but when I go to view an image it is already there loaded. Guess I'll have to turn off preloading previews and thumbnails also. I don't watch video here unless by accident.