Copying the private key only (field ciphertext of the UTC file) will give two different public addresses (one in geth and another in metamask). To solve this problem import de UTC file (present in the node keystore folder) directly in metamask.
When importing a file in metamask, make sure that you have the extension (metamask) running in it's own tab, otherwise it will not import anything.
Opening the extension in a tab (select Expand View
in the ...
menu):

Importing the file:

More details here: https://metamask.zendesk.com/hc/en-us/articles/360015489351-Importing-Accounts