Emersed vs Submerged Growth

I hate to take the discussion away from carriage returns and back to
aquatic plants, but here goes nothing. This past summer I bought 2 E.
Osiris from a local store. Alas, they were not the "red melon swords"
like I wanted, but the pet store owner seemed very proud of himself for
having gotten them, so I bought them anyway. Not having room at the time
for the two of them, I placed one in my tank and the other outside in an
old, rusty barrel that had previously served as a cattle watering tank,
I believe. The barrel had been partially filled with a mixture of sand,
dirt, and decayed leaves and the water was only a few inches deep. It
was sitting in a fairly shady location. I stuck the plant in and forgot
about it. When I returned a few weeks later, I was surprised to find the
plant alive, let alone thriving. Eventually, I forgot about the plant
again, only to remember it on a cold November morning. When I checked
the barrel, all life above water was dead and a thin layer of ice had
formed on the surface. Just to see what would happen, I plucked the
plant out, trimmed all the leaves off, and took it inside and planted it
beside the other E. Osiris which had been tank grown all this time. From
Nov. until now, the outdoor Osiris has caught and passed the indoor one
in size. The leaves are larger and healthier looking too.
Some thoughts:
I was surprised that this plant could stand this much cold. (apprx. 22
Did this plant store up a lot of reserve energy while being grown in the
emersed state, or did it store up a lot of energy while being grown in a
richer substrate?
Possibly, this was just the healthier of the two plants to begin with?
Would this be a typical story for emersed vs submerged plants?