All usernames on Discord have a four-digit number after them called a discriminator, separated from the rest of the name by a # symbol. In the Reddit post in question, that number is #6381.
The problem isn't that the (fake) bot is in the same namespace as users; if there were any problem like that at all, it would be a shortage of discriminators.
However, that's not what this message is saying. It's saying that the name cannot contain "Clyde". In other words, you wouldn't be able to use any name that had the word "Clyde" in it, taken or not.
The fact that they haven't attempted to block usage of "CIyde" and similar does suggest they might not have thought it through, but it's verifiably not a namespace issue.
