According to the OED(Oxford English Dictionary), the noun derives from a verb to kilt, originally meaning "to gird up; to tuck up (the skirts) round the body", itself of Scandinavian origin.

now...where in this original definition does it state a single thing about pleats.

I have also found this:

kilt
–noun
1. any short, pleated skirt, esp. a tartan wraparound, as that worn by men in the Scottish Highlands.
–verb (used with object)
2. to draw or tuck up, as the skirt, about oneself.
3. to provide (a skirt) with kilt pleats.

AND

kilt·ed
–adjective
1. wearing a kilt.
2. gathered in pleats; pleated.

In almost every definition(save the first one) the terms pleated, pleats, or pleating are found.

What does this mean? well I guess that by literal definition that is not a kilt!
in other words it means...
Not a bloody thing...if you like it and its comfortable who cares...

I personally prefer pleats. I also prefer knife pleats to box pleats. But thats personal preference.