A "Showerthought" is a simple term used to describe the thoughts that pop into your head while you're doing everyday things like taking a shower, driving, or just daydreaming. The best ones are thoughts that many people can relate to and they find something funny or interesting in regular stuff.
Tiktok probably generated a unique link to the video just for you when you shared it so that whomever the recipient is will know that you shared it. And then your friend opened said link and tiktok connected the dots and linked the accounts in a DM with the video. Pretty easy for them to do on their end, and they probably see it as a convenient feature to users.
Also, lost fedditors
This is why I always strip everything after the '?' in a URL before sharing it (e.g. ?is_from_webapp=1&sender_device=mobile&sender_web_id=7267504647052363269)
tiktok is a lot more "clever" in that regard. their short links (vm.tiktok.com or whatever) are ALL individualized, there aren't any obvious "tracking parts" you can cut out
Also, lost fedditors
Did they defederate?
The reason to not open unsafe mails.
Their could be links that alert them and multiply their efforts towards scamming you.
Of all the communities, you think this one is the most appropriate?
No shit, but I really thought about this during shower today.
That is why when sharing something you always delete anything in the link after the ? symble.