Firewall: Strange established connection..

Hello,

I have some basic fw rules enabled on new crs router.
Meanwhile I have seen a strange connection under the Connections tab in firewall on winbox.

I have a public IP xx NAT IP yy and a local LAN on zz, lets say.
Connection was from source gg:57690 ; destination yy:80 ; Tcp state Established.
The source IP were from egypt, my location is in europe..

Could someone explain how can someone connect to my nated IP?

Thank you