Fear not the dev is on it, this is from the patreon.
"Hey, we're glad you're enjoying the game so far. We're using flash at the moment because it allows us to achieve what we're trying to do with relative ease and we can reach a large audience by hosting online in browser. Ideally we'd like to move up to a more sophisticated engine in the future (whether this is Unity or not we'll just have to see). Rest assured we are looking into alternatives, although currently HTML5 is looking more likely than Unity unless we expand the scope of the product to be worth picking up an engine as robust as Unity. I hope this answers your question
- Hallows"