Hi Igor,
Yeah this does just look like a proxy. There is no harm that can be done to your website this way, as this literally calls your website and displays it through the App Engine.
As for your comment about indexing, I don't get what you mean, as flawedgate doesn't seem to be indexed. (looking for "flawedgate cardo-ua 17-new-collections" returns me your website, this thread, and nothing about the proxy).
If you still believe there is some abuse and we would need to investigate, I would suggest filling
this form. The proper team will then investigate and take the appropriate measures.
Cheers!