Indeed I have used Dialog flow many years ago. It is really great tool if you are ok using cloud for the inference and it integrates with many things too like Google Assistant etc - really powerful and makes making assistants pretty easy with the UI.
Unfortunately I have not used it recently so unsure if they changed something. Your best bet would be to find a developer relations engineer on that team who can answer your question quickly.  I believe you have to publish it though for it to work beyond the testing sandbox on their website if I remember correctly.
As it is holidays right now you may have to wait until the new year as a lot of people are out but maybe you can find someone on LinkedIn or such who may reply who is on the DialogFlow team.