It's possible it's a dwarf, fish have genetic defects just like humans. Probably more likely it's just not full grown yet or it's stunted.
Have you ever SEEN the mouths on them? They go back about half the length of their head! I think mine's mouth, and he's only a little guy, is bigger than my 9" long severums mouths! So...smaller tetras could very easily be lunch. Bigger stuff should be ok.