They'll all POST requests. I trimmed it out of the log for space, but the first 6 requests on the video looked like (nginx shows the data amount for GET, but not POST):
ip.address - - [07/Apr/2024:23:18:44 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.world"
ip.address- - [07/Apr/2024:23:18:44 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.world"
ip.address - - [07/Apr/2024:23:19:14 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.world"
ip.address - - [07/Apr/2024:23:19:14 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.world"
ip.address - - [07/Apr/2024:23:19:44 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.world"
ip.address - - [07/Apr/2024:23:19:44 +0000] "POST /inbox HTTP/1.1" 200 0 "-" "Lemmy/0.19.3; +https://lemmy.world"
If I was running Lemmy, every second line would say 400, from it rejecting it as a duplicate. In terms of bandwidth, every line represents a full JSON, so I guess it's about 2K minimum for the standard cruft, plus however much for the actual contents of comment (the comment replying to this would've been 8K)
My server just took the requests and dumped the bodies out to a file, and then a script was outputting the object.id, object.type and object.actor into /tmp/demo.txt (which is another confirmation that they were POST requests, of course)
When I've mentioned this issue to admins at lemmy.ca and endlesstalk.org (relevant posts here and here), they've suggested it's a misconfiguration. When I said the same to lemmy.world admins (relevant comment here), they also suggested it was misconfig. I mentioned it again recently on the LW channel, and it was only then was Lemmy itself proposed as a problem. It happens on plenty of servers, but not all of them, so I don't know where the fault lies.