That is really an amazing anecdote but we cannot verify its authenticity
from here.

Not amazing to me at all. Hybrid plants revert to something else all the time.
I have a purportedly dwarf pink Monarda which reverted to the tall red type. A
red butterfly weed which gradually became orange. It is unlikely that a blue
Delphinium would become white, so I think it is more logical to suppose that he
had two seedlings and one died.
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)