Facebook app has many bugs. You can delete the app and install it again. Log out then in again on the app. Go to multitasking and "kill" the app by holding the app icon in the multitask tray and hitting the X. Any of those should fix it if it's showing a different avatar.
For awhile mine would show I have a lot of friends. But when I searched, none were there. Funny I know but I had to try all these different methods and now my friends are there haha.
I had the same issues - mismatched profile pictures and missing friends list... I deleted and reinstalled each time (which was very annoying)... I'll have to try logging out/killing the app if it happens again... Thanks for the tip, Freiteez!