We know they are working on things like US accounts, but I think it’s unlikely this was related. Main reason: the balance showed as US$0.00. This is not how it would be displayed for a US account, it would be $0.00 (in the same way as our balance is normally shown as £0.00, not GB£0.00).
The use of US$ is more consistent with how foreign currencies are shown in UK accounts. Maybe what this hints at is that they are finally implementing the suggestions around showing the balance in a foreign currency when travelling. 