thrown objects on court

[number 26]

happened at my son's high school game 2 nights ago.
team a, home team, in possession. ball in frontcourt. a piece of candy, valentine's day kinda thing, thrown on the court from area where home team's fans are sitting. ref sees the candy skid across the court. immediately blows whistle. turns to that part of crowd. technical. 2 shots to b. loss of ball.

2 questions.

a) how/why would ref assume offender, though obviously seated in team a section, was a team a fan.

b) should not a public p.a. warning have preceeded a technical foul assessment

(after the t, home team coach announced to crowd on the game microphone "you just cost a technical foul..."