tl;dr: what does the word "Resident" mean in a tax treaty
I'm a Belgian PhD Student (F-1) at an accredited US research university. My F-1 visa status officially started in July 2016. From September 2015 until June 2016, I was also in the US as a J-1 Research Scholar at a different institution. I left the US for one week in July in order to get the F-1 visa at my home embassy.
The Belgium-US tax treaty stipulates a two year exemption for students and researchers, which I made use of for my J-1 income from 2015. I am planning to do the same for my J-1 income from 2016.
I'm trying to determine whether I can claim the same exemption for my F-1 income up until September 2017. The key text in the treaty seems to be (Art 19 (2))
An individual who is a resident of a Contracting State at the beginning of his visit to the other Contracting State [and ...] shall be exempt from tax ...
I've been able to determine that I am not a 'US resident for tax purposes'. Even though I would pass the Substantial Presence Test, all my days in the US have been on either a J or F visa, which is exempt from the SPT. What I cannot find a clear answer to is whether 'not being a US resident for tax purposes' automatically implies that I am a 'resident of Belgium for tax purposes'.
Given my visa history and status, would the IRS still consider me a resident of Belgium?