Look at the New Zealand batting lineup. They have explosive batsmen such as Tim Seifert, Rachin Ravindra and Daryl Mitchell. Given this, and given the current state of Zimbabwe bowling, I would say that even a target of 180 is not going to be enough. The only quality bowler in Zimbabwe squad is Blessing Muzarabani. And in recent times, his form has deteriorated considerably. And there are not too many other players there to support him. Given all this, I would expect the Kiwis to win in less than 12 overs.
New Zealand chased down the target of 120 runs in just 13 overs and secured a big win by 8 wickets, losing their two wickets. All the players in the New Zealand squad, especially the batsmen, are T20-style players, so a target of 120 runs is a very easy score for them. Although they lost one wicket for five runs in the beginning, they were able to put pressure on the New Zealand batsmen later, which allowed New Zealand to complete their target of 120 runs in 13.5 overs.
New Zealand has placed themselves as the strongest team in the T20 series. Zimbabwe was already the weakest team to start with but a defensive game, Zimbabwe were able to play their whole 20 overs but only made a small score of 120. New Zealand chasing the small target were sure of the win and wanted to get it as soon as possible.
The tournament would end with a final match between New Zealand and South Africa and New Zealanad would be looking to have an all win tournament. As a preparation for the upcoming T20 world cup next year.