Napoleon was undoubtedly unhappy because he wasn't told the truth.

There was no written doctrine about the French risking artillery if need be; it was more practice than doctrine. Just as they had no official written doctrine on their skirmish tactics in combination with formed troops. Both practices developed over time with usage. For example, Senarmont certainly risked his artillery at Friedland in 'getting up close and shooting fast' and that practice was emulated.

Poniatowski was noted for using artillery in his skirmish line.

Sincerely,
K