I've been a regular-irregular user of CentOS over time an all the times in past from what I remember installing it with CD/DVDs.
Just tried installing it with USB and things got messy. Tried minimal, net-install and DVD iso to the level of getting tired. Everything goes well until the bootloader set-up screen comes up and then set-up goes to hell. It shows error for not founding ISO 9660 on the device. Tried un-mounting and mounting different partitions over '/mnt/isodir' and clicking 'retry' button. Nothing worked.
Either read out following links article#1 (Install from USBKey), article#2 (fix mount image error) and try the solutions/steps in there.
The install boot option from LiveCD/LiveDVD dumped on USB worked just fine for me.