Yup that's right.
A single wall tent is essentially a fly with the floor attached directly to the fly, so there's no netting (or fabric) as a second layer inside the fly.
With the FC UL3 (or any tent with a 30D nylon floor), you're fine without a footprint if you do a quick scan of your site to check for pokey sticks & rocks, and if you're not camping on an abrasive surface like gravel.
The thing I don't like about footprints – especially ones not designed for the tent, is that you often have some of the footprint sneak out from under the tent a bit. This is easy to have happen, as tents can shift/slide around even if you're careful to tuck the footprint in. If it rains and you've got a little footprint poking out, the rain lands ON the footprint and forms a puddle between the footprint and then floor. This is easy to do if you use a tarp etc and it can still happen with an OEM footprint if you get a bad storm with sideways rain etc.
I personally prefer just a more waterproof floor and choosing tent sites that don't contain harmful objects. So no footprints for me, except for car camping when I want to avoid wear on my UL tent caused by gravel, wooden or paved tent sites.