Yeah, I am at a loss at this point. When you run the repolist command I am not seeing it show the EPEL repository, yet when you try to install it it says you already have it.
This isn't really a NodeBB problem though, so we can't really blame the NodeBB script for it. It's almost like Yum itself is messed up. You might be able to get extra help from the CentOS community though, or if someone else here is more of a CentOS expert?