Good question. I think I and Britannica were talking about

different things. When I saw that the boy could sing do, re, mi, I assumed that it was in a fixed-do situation. I think Britannica was thinking about singing in movable-do scale. In this case, neither of our answers were conclusive. That was why I mentioned tonality in the other post. Establishing tonality is the same as what you said "using scale as reference".