..... Did he just pull out a sword because of a pebble?

Yes.

He sorta deflected the pebble with it. The scabbard is a part of his outfit and fixed. So he instinctively pulled the sword out since one of his hands was likely resting on it. If we had a book in hand it'd be more natural to deflect the stone with the book cuz hands would sustain a certain degree of damage, in his case he had his hands on a sword. So yeah he pulled the sword out.