Doesn't seem to be mentioned anywhere but if you are on trial membership you can't download the vault games from the store during the 'free' period running until the 22nd.
The main issues is I had to work this out myself as the person on xbox support chat was completely clueless about the whole offer. After sending her multiple links to the offer details she still kept insisting I had to pay for EA Access first at $4.99. After more than a hour of arguing I gave up.
I have the transcript if anyone at Microsoft cares, shocking introduction into the world of Xbox One.