Zend certified PHP/Magento developer

Why my external IP doesn’t change when I am connected to a VPN?

I am not so into networking and I have the following doubt related VPN connection.

Going to: https://whatismyipaddress.com/

I obtain that my IP address is 151.44.157.246

Ok then I connect to my VPN, it works fine (infact now I can reach some machines that require this kind of connection).

I go again on the same IP address checker: https://whatismyipaddress.com/

I expected to obtain a new IP address (the one provided by my VPN) but I am obtaining the same 151.44.157.246 IP address.

How is it possible? What am I missing? the strange thing is that if I am not conntected to this VPN I can’t access in SSH to this cloud machine while if I am connected to this VPN I can do it.

What is wrong in my reasoning? From what I know using a VPN I go out on Internet with a different IP but probably I am missing something