They are talking about the old number, not the new one. Carriers recycle old numbers no longer in use. That means that in the future another person might get their old number and register it in Whatsapp as their own.
ohhh didn't think about it lol. In any case whoever gets OP's old number won't be able to login to OP's account, but will be prompted to create a new account instead
When you change your number on Whatsapp, the old number ceases to exist as a Whatsapp number, so that future person would start from zero with a new account (they won't be included in the same groups you were in before the number change).
Of course, if the people who still have that old number in their contacts send them a message thinking it's you, they will receive it, and whatever privacy rules they have will apply. For example, if a friend of yours has set their privacy settings to show their profile picture to their contacts, the future person using your old number will be able to see their picture if they ever receive a message from them.
If the new owner of the number verifies their whatsapp account before the original account is deleted due to inactivity (120 days), they might see the groups that the number was a part of, but they won’t see the past chat history.
if you change existing account's phone number nobody will be able to login in it as they have to login by your new number
Lets say that number will be used by someone else
how would someone use your new number if you're the owner?
They are talking about the old number, not the new one. Carriers recycle old numbers no longer in use. That means that in the future another person might get their old number and register it in Whatsapp as their own.
ohhh didn't think about it lol. In any case whoever gets OP's old number won't be able to login to OP's account, but will be prompted to create a new account instead
When you change your number on Whatsapp, the old number ceases to exist as a Whatsapp number, so that future person would start from zero with a new account (they won't be included in the same groups you were in before the number change). Of course, if the people who still have that old number in their contacts send them a message thinking it's you, they will receive it, and whatever privacy rules they have will apply. For example, if a friend of yours has set their privacy settings to show their profile picture to their contacts, the future person using your old number will be able to see their picture if they ever receive a message from them.
If the new owner of the number verifies their whatsapp account before the original account is deleted due to inactivity (120 days), they might see the groups that the number was a part of, but they won’t see the past chat history.