Luke Serna -- who says he's half-Mexican -- admits he handed out tortillas to players, cheerleaders and fans at the big Coronado vs. Orange Glen basketball game as part of a "celebratory action" if Coronado won the game. Serna is a Coronado alum.

The problem ... the Orange Glen basketball team (and the OGHS student body as a whole) is largely Latino.

So, when Coronado -- a predominantly white school -- won the game and people began throwing the tortillas after the final buzzer, many players, coaches, staffers and others were offended ... claiming it felt racist.

But, Serna claims his tortilla plan was inspired by a tradition he learned as a student at UC Santa Barbara, and he had "absolutely no racial intent."

"The tossing of tortillas is used as a celebratory action by the UC Santa Barbara Gauchos at various sporting events including basketball and soccer," Serna said in a letter to the Coronado Unified Governing Board.

"There was not a shred of ill-intent or racial animus in carrying out this celebratory action."

Serna continued, "Those who have enflamed this issue into a racially charged issue should be utterly ASHAMED of themselves."

There has been fallout since the incident ... Coronado head coach JD Laaperi was fired following a school board vote.

Serna believes Laaperi should NOT have been terminated.

"The people who have fallen for this frame-up to smear Coach Laaperi are not worthy of being any part of the discussion regarding this event as it is their intent to try and fan the flames of racism where none existed.”

Serna later told FOX 5 in a separate statement ... "I realize the tortilla throwing has been perceived as racially insensitive. I do not condone racially insensitive behavior, and that was not my intent."