She just had to walk around a bit, presumably because the people at the gate weren't familiar with what to do when someone wants to opt-out.

I guess that qualifies as "not easy", because it's a meaningless statement that can be justified by the slightest inconvenience.

I think "easy" should at the very least include "you're notified that it's even possible".

requiring opting out is a huge barrier as shown in behavioural economics and definitely makes it "not easy" especially if no one else is seen to be doing it

You can define it (imo) in two ways.

One is by legible criteria: how long does it take & such. The other way is: how likely people are to do it. That's how a UI design would be measured. How many more people sign up if I remove the "age" field from a form. How many fewer people become organ donate if you need to register online vs tick (or untick) a box on your lisence form?

The first way is how a regulator or judge would see it. The second is often the one that matters to how things develop practically. Eg how gdpr-ish consent actually affects realities of user control over their data.

A common pattern is to concede the first, and rely on the second to make it irrelevant. Opt out is available, but the "UI" design ensures that it's rare.