In a contract in which the "parties" are businesses, corporations etc. - as distinct from private individuals - the expression "ajenas a" refers to anyone who is not operating under the responsibility of the contracting party (where 'anyone' may refer, for example, to an employee of the party or to a subcontractor (which may of course be another business). It would be perfectly normal, under a contract between businesses, for the employees (and legitimate sub-contractors) of each party to have knowledge of certain information (preferably on a 'need to know' basis) - if only so they can play their respective part in fulfilling the obligations of said contract.

"not affiliated with" is one way of expressing the idea that access to senstitive information must be restricted to those who have a legitimate interest/responsibility in the respective party's involvement in fulfilment of the contract - be they the 'party' itself, or anyone working under their contractual responsibility.