Polymer 2 iron-ajax is loading the wrong local file - polymer

Question

When loading a local json file with the iron-ajax Polymer web component the response returned is the contents of index.html, not the json file.
<iron-ajax auto url="data.json" on-response="handleResponse" handle-as="json"></iron-ajax>
I am checking the response in Chrome developer tools under "Network" and the response given is the same as the index.html file. I am using Polymer 2.0 starter kit as a front end with Flask on the back end. Apologies if this is a simple mistake but I am new to JavaScript.
My simplified file structure looks like:
/app
|-- app.py
|-- /static
|-- index.html
|-- /bower_components
|-- /src
|-- data.json *(file to be loaded)*
|-- my-app.html
|-- my-view.html *(view to load file)*
EDIT:
I believe the problem may be to do with this catch-all in the app.py file from the boiler plate I am using. I realise I do not understand how the relative url's are working in this application.
#app.route("/static/<path:path>")
def static_c(path):
return current_app.send_static_file(path)
#app.route('/', defaults={'path': ''})
#app.route('/<path:path>')
def catch_all(path):
return current_app.send_static_file("index.html")