Smith wasn't the captain in his first Test. He did become one when he was really young though. The only real answer I can think of is that Gibbs was probably viewed as non-viable because of his role in the match-fixing scandal, Kirsten was about to retire and they probably didn't want to burden Boucher, so there weren't a lot of viable captaincy options for South Africa after Pollock was sacked.
For Germon, CricInfo says:
"After the controversy during the tour of RSA in 1994-5 and the poor form during the home centenary season immediately following that, the administration of the New Zealand game at the top level fell apart. Part of the shake-up involved appointing a new coach (Glenn Turner) and this, in turn, led to a change of New Zealand captain. Turner wanted someone with proven leadership skills, who had the respect of the players, and who could maintain discipline both on and off the field by his own example. He had no hesitation in going for Lee Germon, a player with no previous Test experience, but who had been on the tour of South Africa and had proven leadership skills at provincial level"