What? 2 seconds? That sounds crazy. It either breaks ongoing connections or wastes addresses since you would have to keep your old one until all connections are closed.
It probably wasn't really "issuing a new IP address" per se, but rather CGNAT, where your apparent IP from the perspective of an IP reflector would be the IP of whichever NAT gateway your outgoing connection had been round-robin-load-balanced onto. Under CGNAT, you don't really have any single public IP; or rather, in another sense, you (and 100k other people) "have" all N public IPs at once — just like devices on a NATed home network all share the one IP address assigned to the gateway router in front of the NAT, and would all "have" multiple addresses if that gateway-router were multi-homed.