Different contacts with same phone number?

I’ve had 2 instances now where I receive a phone number from a NEW friend. I go to add them to my contacts and it appears they are somehow ALREADY in my contacts but with a different phone number. Very odd. Also, in both instances, old text threads pop up associated with the number. The texts are with entirely different people (NOT the new friend) but YET they happen to have the same first name!

So as example, I meet new friend named Jim, add him to my contacts, and see a phone number already there, plus an old text thread with “Jim” but an entirely different Jim, who was a person from a car dealership many states away where I bought my last car.

How can this be???