I have a humane feral cat trap from the time when I trapped Lucy and her boys (Lucy brought her kits into my verandah where I fed them till I noticed signs of 'flu).
Looking at it from a Fred-cat point of view, I think he got carried away exploring a new territory which has different creatures and cats in it. I don't know if he's seen a squirrel before. During this adventure, I think he just forgot about home, being able to find food on the squirrel feeding tables which a neighbour puts scraps on. There are lots of birds here whereas the last area was virtually bird free because of so many cats.
After a few days, his old feral nature kicked in and I think it will stay unless action is taken. He won't live long as a feral as there are no colonies or feral feeders locally, so I think it's best to stop the process now, whether he likes it or not, for his own good. As a domestic he has regular meals and health care plus his own little colony of cats.
None of the cats are 100% domestic, they all retain something of their feral natures. Lately, Victoria has been sleeping with me; every morning I wake to find her snuggled into my tum, but I know that feral Victoria is still there, she has just learned that good things come from me: food, warmth, love, etc, so she stays.
Fred wants to come in, but is scared. So trapping him is just a way of overcoming his fear. He'll hate me for it till he has his first good meal. Then he'll notice the warmth, the other cats, the regular food etc...
I've got men coming to change the boiler tomorrow morning, they'll be here for two days. I might shut Fred into one of the rooms with least unpacked stuff in until they've gone. He'll hate me for a while, but I'm sure he'll come round. Meanwhile I'll arrange to have the flap installed asap.
So later tonight, in a couple of hours when the others are in, I'll bait the trap in the bushes where he's been seen.
Years ago, for the first year or so of living with me, Fred was defensive to the point of vicious, which is why he didn't find a home. He's come a long way since then and I don't want him going back to that state.