It sounds like the system is a little confused. Those 2K miles are likely what would be needed to reach 24K miles, which is the alternative way of reaching Silver (if you didnt fly those two A3 segments).

It may just take a day or two for the system to realize that you qualified and upgrade you to silver. That delay is pretty typical, though I would expect the website to not mention any further requirements for qualification. I'd wait one or two days and re-check - chances are that this will fix itself.