Welcome to FlyerTalk, coflyer 1962.

The mere fact that they were connecting from an international flight doesn't automatically gain them access to the Prsident's Club. Also PTY is not a BusinessFirst market so even if they were flying up front those flights are considered International Business and not BusinessFirst so PC access is not included. The only way for them to have accessed the PC on their layover in IAH is if they are Star Alliance Gold (CO Gold Elite or higher. UA Premier Executive or higher...) or if they have membership for the President's Club, UA RCC, etc., or hold an American Expreess Platinum (or higher) card. There is also a program called Priority Pass which I believe CO PCs are among the lounges a member of that program can use.