Is it a wild rabbit or a domestic that got loose?

Wild rabbits can dig and get out with no problem. The color of their fur camouflages with the terrain.

If it's a domestic rabbit (black, white, spotted..etc..) they don't have a camouflage and I wouldn't recommend letting it loose. You can always catch it and give it to the SPCA.

It's a wild rabbit.

He must be able to get out, as he got in there, or he was born there and the rest of the family left. Right?

He entered as a baby, I assume he came in when the gate was open.
The garden is enclosed by a fence about 10 feet high. Certainly the gophers, ground hogs etc manage to dig in. But recently we've been securing the border, so not so easy to get in - or out.

My thinking is the little fellow doesn't know how to get out, or that there IS an "out". Now he appears to be full size.

Open the gate during the day?

Can't leave the gate open except when I am there. Otherewise people might take things, plus- maybe more rabbits would move in!
Yesterday I was at the garden, and I didn't see him (or her).
so maybe the rabbit does go in and out.
hope so!

We have many wild rabbit in our habitay who rove freely. They are so tame that they follow us around like cats. They even seem top know their names. They will sit by our sides and eat from our hands. We have no desire to harm them as we have a wildlife habitat. We are most happy when they deliver their babies. In the winter they have shelter for them.