The plagioclase, olivine and pyroxene had to have formed at some depth, and the current body is much to small for that.
“The analysis suggests that Itokawa was born from a larger body that formed 4.6 billion years ago. Then, about 1.5 billion years ago, a large collision tore that body apart and some of the remnants eventually stuck together to form Itokawa”
The observation re fomation of olivene might be part of their analysis.