The shed is fairly new and as far as I know, doesn't have any access holes in it. In fact, there's never even been a mouse in it. So the cat must have snuck in when the door was last open. The thing is, the last time I remember being in that shed was over two weeks ago when I went to get some tools. There is an outside chance ( but I don't remember and don't think so) I was in it briefly about 10 days ago when I cleaned my car out, but even then, isn't 10 days a long time to go without food and water? I can see that it had messed up the venetian blinds I have covering the windows, so it was definitely trapped in there for at least 10 days.
It finally came out after some coaxing but then my dog spooked it and it made a bee-line for the nearest tree which in it's weakened condition, it could barely jump up on. I keep some cat food in the house to feed the odd stray on the coldest days of winter but when I took it and some water to the backyard, the cat was gone ... hopefully to it's home.
The only thing I can think of is that it found some insects to eat. I thought a human couldn't live more than 3 or 4 days without water ... could cats be different?