Once rebooted, you need to enter your PIN to unlock the phone (and the SIM as well). Before that it is not possible to unlock the phone with biometric credentials (face ID or fingerprint).
As far as I'm aware, police can force you to hand over your biometric credentials (they can hold the phone to your face to unlock it when you have face ID enabled, or can move your finger to the fingerprint sensor). But they can't force you to reveal the PIN number.
What a bad article. I mean, good for him, but expected that there was a further insight of how people are attached to their phones, other than just a single quote in the headline.
Here is another, similar story of someone that has been incarcerated for 44 years which gives more insight into the changes that have been happening while being locked up in prison, although the article focuses more around legislative implications.