Its working because your IPs are connected to the same network.. So does not matter what interface pfsense sends traffic from be its lan or its wan it can still talk to your actual physical gateway.
So if you look at its routing table - what does its show as primary route to 172.16.1.1 which I assume is your actual physical gateway off your network. What interface is it using?
Here is your problem - a client connected to lan side of pfsense can directly talk to 172.16.1.1 - there is no reason for it to talk to pfsense IP - unless you tell it too. Because your lan side is bridged to the same physical interface as your wan interface.
Why in the world would you setup such a pointless setup?