If you install some rpm without yum (rpm -Uvh), you should see the following error:
...
Transaction Test Succeeded
Running Transaction
Warning: RPMDB altered outside of yum.
Installing : whatever.x86_64
...
This is because the yum database (/var/lib/yum/*) is out of sync with the rpm database (/var/lib/rpm/*), and to fix it you can execute:
yum history new
You can also wait to install another package, then yum will resync the databases