The Coast Road

I'm reading The Coast Road by Paul Gogarty. It's borrowed from the library and contains the scribbled thoughts of a fellow lender in the margins...

Page 5
- Gogarty says: "There are more castles in Kent than in any other country"
- Scribbler says: "Cumberland and Northumberland?"

Page 16
- Gogarty says: "A sliver of new moon is rising"
- Scribbler says: "The new moon sets"

... Why would someone do this?