Understanding Finite Field

Please see this video

YouTube - WildTrig20: Trigonometry with Finite Fields (II)

At around 8:40 it is said that Q(A,B) + Q(A,C) = Q(B,C) so the given points form a right triangle

But shouldn't it be Q(A,B) + Q(B,C) = Q(A,C)?

Furthermore I don't think that's even a right angled triangle since Q(A,B) + Q(B,C) != Q(A,C) [i.e., 5 + 25 != 34]

What is he trying to say?

I have posted it in this forum because this video is trying to explain the basic properties of Finite Fields (7 in this case)

PS: != means "not equal to"

Thanks in Advance

:)