Well, basically any president would have been that popular after 9/11.
As far as the low rating is concerned...well...he is responsible for that.
I saw a Presidential historian talking about it once...he mentioned the fact that Bush held the high approvals beyond a year and half after...and then got a second boost from Iraq in 2003...made him extremely popular from September 2001 to January 2004. Yes, 9/11/01 was the trigger...but his popularity peaked around November 2001, shortly before Thanksgiving...a good two months after the attacks, and his high popularity remained for all of 2002, and just about all of 2003.