If you have the option to look at your report today compared to a previous report I would suspect there was a change. A balance decrease while having a card report a balance would not be the cause of the decrease. The recurring answer to this is that something else happened.
The balance decrease was an alertable event so you received an update to your score. This is a topic that pops up daily where it is thought the alertable event is the reason for the score change when it seldom is. Many people on the forum have expressed their frustration with MyFICO due to this and the confusion it causes.
Since it's TU you should be able to look at your CK report from a past week and compare it to your most recent report if you do not have a before and after with MyFICO. The score could have changed some time ago as my experience has been that score updates are not always timely as I can clearly see with my EX subscription compared to MyFICO subscription.
I saw the same thing while looking at my AMEX FICO today, but in my case it was due to a new CC from Wells Fargo with a HP along with a HP for a mortgage refinance inquiry. Good news is with a little gardening they'll be back in no time. Have a drink on me...
