One more question, Michelle: your sig line also calls the manuscript a WIP. Is it actually finished?
I can think of a couple of things here:
One, if you're still writing or revising, it's premature to be approaching any agents with it. And if that's the case, the agent in question may have sensed that the work isn't ready yet.**
Two, it looks like the entire manuscript, or a significant portion of it, is online there at Wattpad. If that's true, a lot of agents consider that a form of self-publishing, which can really hurt your chances of getting them interested in representing you for English first print rights. Obviously that's not true across the board, but it's usually not considered a good idea to have your work posted online like that when you're querying -- or before then either. Agents are interested in selling those first print rights, and if you've published it already, well, those are gone.
**Correction, I recall now that you're querying nonfiction. I take back what I said about the manuscript needing to be finished. Sorry, I'm short on sleep today.