Yes, I encountered that a lot. Someone adding me for no reason.
I just delete the group whenever I see one that I'm not familiar of.
I haven't change my settings as I'm too lazy. Thanks for that reminder.
But, I really don't invest based on how big the telegram community is.
We all know that some projects are getting services from third party to increase the number of their members.
You will notice that once the IEO or ICO is finished, most of them will delete the account or not active anymore.