I think the PopCap games are supposed to be part of EA Access. In the Xbox One Store there is an EA Access ad that says that PopCap games are now in The Vault. The games all work for me still. I have EA Access. I haven't seen any official announcement of these being added to EA Access. I think it was a screw up when anyone could download them. I expect there will be an announcement of the added games to The Vault for EA Access at some point soon.
I've had that happen a few times. It seems to happen if I click the "Try for free" and then have to log in. If I'm already logged in and then click that button it seems to offer the $0.00 price. Best to check every time. If it isn't free, try the button again until it is.