Giant leaf on Sedirea japonica

[LexaCat]

Hi All - I purchased a Sedirea (Phal) japonica last fall and have been growing it under LED lights for the past 7 months. I am happy that it has made a new leaf in that time, but the size of the leaf is out of proportion with the rest of the plant. The leaves that the plant came with are smaller and rounder whereas the new leaf is very long and a little thinner. Has anyone seen this before? Could it be because of too much light? Thanks in advance for your advice!