The reasons some users mentioned only make sense if there were only 1 or 2 cases listed on that website that were like this. But since there are a lot of them (73 right now) it can't be explained that easily. All I can say is that the bitnodes.io website in my experience, has had fake nodes listed for some reason. For example a while ago I was trying to test syncing and some other stuff and when I tried connecting to some of the nodes listed there using my own code, I realized their list contains fake nodes that even though the site may say they are synced, they do not capable of providing you with any data (eg. with block headers).