Upon opening a pack of the Final Fantasy expansion, my account was given the "Set Collector 1" achievement despite me not having obtained at least 1 copy of every card from a set. (See screenshots below). I also checked my collection to see if it was maybe counting a bonus sheet, but I haven't fully completed any bonus sheet either.

I encountered this error on a Windows 10 device.

If anyone knows why this could have occurred, please let me know!