I did wonder that myself.
The article states "was able to use to unlock an iPhone", but then goes on to say
"The key question, however, is whether the thumbprint matches Minister von der Leyen's actual digit – and she's unlikely to offer herself up to check."
Which leads me to believe (perhaps incorrectly) that to test it, he used the fake print to set the touchID pattern on his phone, and to also unlock it 'proving' it works, or (very unlikely) that he asked her if he could borrow her phone for a few seconds.
Which (to me at least) only proves that he was able to fabricate a pattern that would be accepted by the sensor, when placed over a finger (to provide the previously mentioned heat/pulse), not, that he has been able to clone someone's prints from a photo.