A little disconcerting

I'm reading Assassins, book number eleventy-seven times infinity in the Left Behind series.

I just flipped it open and noticed and inscription on the frontispiece. It reads:

Dad,

It was great to have you here. I hope you will enjoy this one.

Love

Scott and Kay

Christmas '99

The thing that makes that a little creepy is that this is a library book.

Did Scott and Kay write a little loving message to Dad in a library book? That would be queer.

Or did someone give the book to the library and it magically became a book to lend instead of one of the books they sell at the front for a $1.50 for hardbacks?

Did Dad not enjoy the book? What happened here?