I'm sure if it were a cow they would have recognised it as such. They are pretty unmistakable afterall, and their behavior patterns are consistant. Cows are incredibly stupid animals. They wouldn't have a clue about keeping up an equal pace with someone. Also, they either move away from people, charge them, or act like they will charge them. But 99% of the time they will move away. And they don't hang out on beaches!
I don't know what they saw but clearly it was intelligent and not anything normal. The mind naturally wants something to turn out to be normal, but clearly what they observed kept shattering their ideas about how its probably something normal like a cow or bear. The weird thing is about it looking right at them. Don't cows have eyes sort of closer to the side of their head, rather than straight on the front? I don't think cows can look straight at anything, can they? My brother has a lot of cows, perhaps I'll take a closer look next time at how they look at people. I've been around cows quite a bit though, when visiting my brother, and I can't imagine a cow behaving like whatever this thing was. They are slow and lazy creatures who just like to eat grass and can't be bothered to do anything but that.