The humidity has been pretty low the last couple of days(at least where I am, and presumably where you were). Even though you’re not noticeably sweating, you can lose a lot of water in two hours wandering around the woods (if it was also breezy, that would exacerbate the effect). The leg cramps would be consistent with dehydration. Maybe 4lbs of water in 2hrs wasn’t enough (assuming you were drinking it and not just carrying it around).
That's a pretty good possibility. It was warm and breezy, and although I was drinking water, it doesn't seem to absorb as well coming out of the winter months. And skipping lunch that day may have had something to do with the bonks 24h later.