I don't know if I would call it "stealing a spot" more like "stealing the show" maybe
With that said, I have experienced this before. I've seen it fishing in a boat and some days it seems someone just cannot hold the rod right. The next day, it is the other way around. More to do with jigging. As for fishing with a float, there might have been a number of factors that contribute to the "why" in your case.
First, I would say that it could very well have had something to do with what was on his hands. Did he stop and pump gas, put sun screen on, bug spray... it could be anything. The other thing is sometimes as simple as the color of the float. Was yours clear and his orange... or yours chartreuse. Sometimes it can be the smallest of things. Were you using a an Aberdeen hook and him using a bronze hook? Was he using 1/64 oz split shot while you were using 1/32 oz.
There are days when it doesn't seem to matter. I think what really separates good fishermen from guys that go out and catch fish is the details they pay attention to. If you take a closer look at the situation, things might not be all as they seem to be. As a good fisherman, if you can figure out the "why" you have won the battle! He may have had different minnows, purchased at a different bait shop. Sometimes it is the smallest of details that "could" make all the difference. Of course, we will never really know for sure, but I'd be willing to bet that something was slightly different.