My two cents ...
Lighting could definately be a factor. Also as those before me mentioned genetics. The first time I bought autos I got Speedy Gonzales from Flash seeds. I got three fem seeds, one of which germinated and had the same problem yours did (under 700w CFL and 150W HPS). I dubbed him 'retard' as it only grew several inches and produced enough bud for a bowl. The second time around I got some seeds from Short Stuff (auto-assassin and snow ryder). They are now frickin huge and will provide about an oz each.