Adding a new CC doesn't always cause your FICO to drop. While it is well known that FICO benefits a lot with your first, and to a lesser degree second, CC, My FICO just jumped from 690 to 736 when I added a WM CC. It wasn't Util which stayed at 11%. The CL is .8k so my total CLs went from 52k to 53k.
However, this set of reasons is funny:
Your FICO score may have gone up because the following 2 factors are not hurting your FICO score as much as before:
You have too many credit accounts with balances.
You have not established a long revolving credit history.
See the "Extreme rebucketing" post for more background.