IANAL but this seems to be pretty common all across the world. The usual recommendation is to put your phone in "lockdown" mode if there's any suspicion you may get arrested. This prevents the phone from being unlocked with biometrics and require pin.
You can do this either by restarting or turning off your phone, or a button combination (power + volume up on my android) and selecting lockdown.
Also for iPhone:
If you press just the side button/lock button five times in quick succession, it will also go into lockdown mode and can only be unlocked with a pin. A little easier to covertly do as it’s just a button mash before you get nabbed.
At least on my stock Android Pixel you cannot use biometrics to unlock after a restart. So if you just hold down the power button to shut off the phone it would require a pin after booting.
We're talking about a hypothetical situation where you know you're potentially about to get arrested. I doubt you'd be powering it off and then on again while you talk to the cops.
If you get arrested in NZ they can search your phone and impeding them is impeding a search. As far as I know the courts haven't intepreted the right to not self incriminate as extending to passwords, so the difference in the article is immaterial.
If you're using Android you can automate lockdown mode using Tasker so that it can it can be enabled "passively". For example, on my phone lockdown happens after: too many incorrect access attempts (bad biometric or passcode), any Bluetooth disconnects, any sudden shakes or jolts. So if someone takes my phone away from me, takes my phone from my car, or if I turn off my watch then lockdown. If someone fails to unlock my phone: photo taken, synced to cloud, phone lockdown. If my phone gets tapped, set down a little to roughly, or I get thrown to the ground or against a car with my phone in my pocket then lockdown. Sure, it means biometrics is often disabled on my phone, but now I find that reassuring.