Well, I can;t say for SURE (and I don;t want to mislead anyone) but it looks like that petiole may have just the slightest touch of lighter colored tissue embedded in it that translated to a little pigment streaking on the new leaf. Especially the far left edge of the upper leaf blade. If it is a slight tendency to variegated, it probably won;t last. It looks kind of like the speckling pattern on the one referred to as Thai Constellation.
Your plant is a tissue cultured plant, it may have gotten a little variegated tissue in the mix.
