My best guess is you forgot to include some sort of contact information with the submission. But you did email it, so the agent could have easily emailed asking for the info. So my answer is: no idea.
I don't see the harm is calling back the number. As you said, they didn't leave a message, and if someone picks up, just say, "I received a call from this number, yadda yadda, I was just calling back to...blah blah." It could be something, it could be nothing.
Best way to find out is to call. Or look it up in a reverse directory.