This clip is from an episode of the TED Radio Hour podcast. This is a great podcast which looks in more detail at well known (and not so well known) TED Talks. This episode looks at whether humans naturally want to help others.
For context – the audience has just seen a clip of someone who needed help being ignored by passers-by (people walking past at the time of the incident).
…I would not have done that…
The speaker is using the structure would have + past participle to talk about the hypothetical/unreal past.
The audience has just seen a video of people ignoring someone who needs help. They were not there at the time, but they can imagine being there, and they can imagine their actions. You can think of this as part of a third conditional: (If I had been there) I would not have done that.
Here’s a similar example. Imagine you are talking about your boss deciding to fire someone yesterday. You disagree with the decision. You might say: “I wouldn’t have fired her” or “I would have given her another chance”. The sentence refers to the hypothetical/unreal past because you aren’t the boss, and it wasn’t your decision.