Mini tomato plant?

[cloz]

I started some tomato seeds that I had saved last fall from 2 tomatoes off the same plant. They were started about mid January using the coffee filter method. I transplanted the germinated seeds to this 6 pack and they have been growing under flourescents until about a week ago. All is well with 3 of them but one plant is noticeably smaller and a different color than the other 3. Any idea what could cause the difference? Just a weak plant? The little one seems to be growing just fine , although very slowly compared to the others. The variety is Red Cherry Large (I am guessing the Ferry Morse seeds). I purchased the plants last year at a garden center. I will try to upload a picture.
I may not plant these because I have more than I need started in the trays in the second picture. I will have plenty to give away to friends and relatives as I will be planting about 60 plants.
I am just curious as to the difference in growth since I know the seeds came from the same plant.