Calling old people grandma and grandpa…

I have a son whose almost three and he has a speech delay, I’m not really sure if that’s relevant or not.

So he calls his actual grandparents grandma and grandpa, but now he calls anyone who is on the older side grandma and grandpa. Like at the supermarket any older woman he sees, he says “hi grandma!” He calls our next store neighbor grandpa. Last night he called my husbands coworker grandma which was pretty bad, because she is older than us, but not old enough to be a grandma.

He just started saying grandma and grandpa recently like 4 months ago, so maybe because it’s new? How can I get him to stop?

And now I also worry, can he not tell the difference between his actual grandparents, and strangers? Has anyone else’s kid done this?

Edit to add- I meant to post this in the baby toddler section, sorry I know wrong group lol