Installed mint on disk now mint on another disk wont boot

[confusious]

I just installed mint on my /dev/sda drive using lux encryption so I could not manually install and let the installer do all the work (partitioning etc.) While installing I kept my external drive with linux already on it plugged into the computer. After the installation the fresh install on /dev/sda works fine but my old mint installation on the external drive won't boot now on /dev/sdc. I get the following:

efibootmgr.png

I accidently deleted the picture of the actual error but it said something like the boot loader couldn't be found. So gparted didn't show /boot for /dev/sdc1 which was the efi partition for my old os that no longer boots. I was trying to fix this problem on my own and now I really messed up the mount point as shown in the following pics. I have no idea why the installer changed another disk. I was notified when the install began that /dev/sdc was mounted which worried me at first but I left it mounted because it said nothing can be changed on this disk when mounted. Can anyone tell me if there is something I don't see? If it is the boot loader how could I reinstall it without a complete fresh install? Or could this simply be due to the fact that /dev/sdc installation has no /boot or /efi labeled under the mount point anymore?

sdc.png

sdc1.png