If it does indeed mean 'friend', then all that proves is that Gaelic is an Indo-European language; which we knew. And, since Latin was only recently discontinued as a liturgical language and a school subject, I would bet on the familiarity of carus/cara = dear, beloved as a factor in the word's usage as a name in
Ireland. Of course,
Cara has also been used elsewhere, but there isn't much connection between Italian and English name usage so my bet is on Latin.