If you do all of those things in one day, that's great. The purpose of this challenge is to open up to alternative forms of exercise instead of doing the same one each day (I've been doing the bike every day since I've started and I've had days that it seems boring, know what I mean?). This keeps things fresh. Instead of saying "I don't feel like exercising today, I'm tired of it" it'll be turned around to "I don't feel like doing that exercise today, so I'll try this one."
So, like you said, you can count walking for one day, even if you do it every day, but you can't turn around and claim it later on the week. If you do zumba multiple days through the week, you can count that another day. Just don't get caught doing exercises later in the week that you can't claim because you did so in previous days.
This should be a fairly easy challenge, seeing as we're supposed to do 30 mins-1 hr of exercise for points anyway. So these exercises can count part of your time so you're not doing an hour and then turning around and adding to that with the challenge. I know a lot of people are busy with work, families, etc and don't have much spare time after that hour of exercise.