Horizontal Dahlia Sport?

This is the dahlia I planted horizontally to get it deeper in the ground. I wanted to get some adventitious roots all at the same depth; plus some extra stems. It's still early days. But the results so far are somewhat strange, to say the least.

After laying the plant in the hole and completely burying it, it took some while to emerge. But when it did, three shoots broke through the surface at roughly the same time.

However, as you can see (I hope), only one of the three is really romping away. And when I say 'romping', I mean 'ROMPING'. Considering this plant is a short variety, and considering it is on the dry side of the bed and has received absolutely no water from me, it is doing very well indeed - certainly much better than the other two.

Not only is the stem thicker, and the leaf much larger, the leaf is also a slightly different colour (it's lighter and greener - the others are bronze), leading me to suspect the plant might have thrown a sport (an uncharacteristic shoot on the parent plant). I don't know yet. Will have to wait see. However, it's not the only plant which has produced large leaves and thicker stems - one of the 'wheels' has, as well.