DHCP Relay Assistance Please

Imagine the topology of my network as this:

hosts --> layer 2 --> core switch --Layer3--> firepower box --Layer3--- > DHCP server. 

Originally the firepower box was a pair of 5580's, and I've migrated them to firepower firewalls. Works fine. However, I was reviewing my config tonight (3 weeks after my migration) and I realised I had forgot to put DHCP relay config on the firepower boxes. YET, the DHCP service is issuing new IP's without issue. This has just defied my logic of how DHCP relay works. Currently the core switches have a DHCP relay configured to point at the DHCP server. But the firepower box has 0 DHCP relay config. I thought all layer 3 devices in the transit path towards the DHCP server required a relay agent. Is this not the case? What magic is happening here.