It's very likely that they could pursue you legally for releasing your app in the same space after working on theirs. They might be ultimately destined to lose, but they'd pursue you based on the fact that you don't have the resources to fight them.

So by signing this NDA, you are very likely (in effect) saying that you won't release your app or discuss it. It depends on the exact wording, though.

If your app is important to you, you need do one or more of the following:

1. Ask the company directly about the release of your app and get it in writing that your app is not their property and that you can release it without violating agreements with them.

2. Talk to a lawyer

(I'm not a lawyer and am not giving you legal advice)