When my baby was born with triangular hallux nails I thought it was 'normal' and reasoned that it must have been as a result of rapid growth. for example: when the nail started developing it was only 2.5mm wide, by the time this reached the top the base was 5mm, as the entire toe was also larger, thus making a triangle shape nail. Also I didn't consider the lateral folds to be hypertrophic, especially not more so at the distal end....
I did have other things on my mind then too though, but is this such a crazy theory?