My math professor held up a little cartoon drawing the other day. Depicted was a kid rather like you who held up his hand and said, and I quote, "I have something completely irrelevant to say for the purpose of impressing you that will waste everyone's time". That is what you did.
Your 'scientific' mind may scoff at bypassing the lost energy/mass in the form of light, but my 'engineering' mind says that the amount of energy lost would be tremendously obscured by any macroscopic application that would involve conservation of mass application. Indeed, the amount of energy lost to light would be eclipsed by the amount of energy lost to sound/vibrational energy in whatever process occurred in the closed system. So frankly, not only were you wrong to interrupt the class, but you didn't even focus your attention on the largest loss of energy/mass.
I also call into doubt your story of the teacher's reactions. History is written by the victors. Sounds to me like another example of student-run classrooms.
As for the topic at hand, when the instructor is wrong, I point it out humbly and respectfully if I feel it's a grave enough error. Usually I'm wrong, unless it's a sign error.