I didn’t find anything. There is just the license agreement in that place which doesn’t seem to make any reference to OSM.

Did you look where (s)he indicated or at the right place? Settings-General-About lists (zillions) of licenses for projects used in iOS itself. If I understand this correctly, this is about the new iPhoto app. The Numbers and Pages apps have an 'Acknowledgements' page in the Settings app. Is that where you looked?

Yep, that’s where I looked.