This is not the official text.
As you have pointed out, this additional line is not in the PHB, nor in the documents published under license. It also does not appear on the D & DBeyond page of the Warlock class, which contains errata, and this site is considered a more reliable source than unofficial D & D wikias.
The unofficial wikia seems to have adapted the 2019 text Sage Advice Compendium (available on the WOTC website), or possibly from original tweet Jeremy Crawford, game designer, and added this text to their input for The eyes of the rune keeper.
Apparently, some users of this site have copypased the combined text of the unofficial wikia, or may have copied it.