I had been under the impression that the associations went the other way - that the Latin Dexter came from the Indo-European as did the Latin Sinestra. From those, we derived the association of the right hand with dexterity (so a person with 2 right hands is ambidextrous whereas a person with 2 left feet is clumsy) and the sneaky connotations of "sinister" (as you watch the person's right hand to ensure he will not attack you; a sinister person might stab with the left hand by surprise).