Very likely he was a bit overstimulated and feeling the need to destress (good excitement is still stressful to a dog). It's still terribly rude. How many times have you seen a dog deliberately mark another dog? Not accidentally peeing on them while marking over that dog's "spot", but walking right up to a dog and peeing on their leg or shoulder. So this is a "zero tolerance" thing for me. I also don't allow random peeing on people stuff, even outdoors. I lead them to a tree, bush, or just stand in the grass, rather than lightposts, etc. Sometimes you do just get a dog that's determined, but at least one has a place to start working if there's clear boundaries and an easy, right alternative. It's easier to teach a dog "do" than "don't." 
If I were working with Neiko, I'd watch for future signs that he was mildly hyperstimulated under similar circumstances and make sure he had a job to focus on rather than pooting around at random (stay with me, down stays, random recalls with big rewards). At some point he'd switch from bouncing around seeking a release from tension, to seeing whether you could offer something that gave him the same relief. It's not a permanent thing, just something to get him past the WHEEE stage that a lot of young herding dogs go through.
I totally feel your pain. Ted's in that phase (he's two). He thoroughly embarrassed me this weekend when he first went off and freelanced with the sheep while the farm sitter was here, and second, slipped under the front gate to bark at our landlord who was getting stuff out of the barn (seen him a million times doing the same thing). But, there were twice as many dogs here that weekend as usual, and I wasn't here and the housesitter was, and she's really cool and so are her dogs, and WHEEEEEE his brains apparently dropped out his ears at some point. It's normal.
Becca Shouse: Irena Farm, Semora, NC
Cord, Ted, Gus, Zhi, Maggie, Lynn, Lu, Min and Tully
Waiting: Bubo & Ben
"We didn't have a phone, and we couldn't call you!" Helen, AIDS orphan. Don't let them die of ignorance - WorldHelp.net
"I-Dog Biggest Loser" Official Cheerleader/Mascot
Start 09/15/08: 186.4 lbs Current 185.5 lbs