Why a PLA5236 can assign an IP address to a device?
This is PLA5236 design behavior.
If there is no DHCP OFFER packet sent to PLA5236, the PLA's DHCP server will be enabled.
In this topology, there is no router (DHCP server) connected with the PLA5236. So, the PLA5236 will activate it's DHCP server to assign IP-addresses to the laptop which is connected to the PL5236.
In contrast, PLA5236 will disable it's DHCP-server function when it detected a DHCP server/router in the environment.
In this case, the Laptop's IP address will be assigned from the Router(DHCP server).