Originally, the minimum length for a segment was much shorter. After a while, they realized that short segments were problematic because the accuracy of GPS units and recording wasn't good enough to accurately track times over short distances. With short segments, there are only a few data points and if one or two of those are a little off, it makes the results totally wrong. So, eventually, they changed the minimum length of a segment that you could create, but they left the short ones that were already in the system which is why you will still see some that are shorter than anything you could create today.