Yes. Trademark law says the use of a trademark as a trademark is an issue. Using the discord logo to link to a discord channel is fine. Allowing a site to be named Discord with a different TLD is using a trademark as a trademark and that can have consequences. The whole point of trademark is to distinguish goods/services and by failing to prevent the use of discord.io they kinda dropping the ball here in my opinion.
No, it’s still trademark infringement. Especially since it relates to the same product. It would be different if they were unrelated but this is about as bad as infringement and brand confusion can get. Any competent legal OR marketing team would have sent them a C&D ages ago.