Probably because it is short-term.

Security was held exactly one year which is short-term. Long term is more than one year.  One more day would have made it long-term.

per TaxBook "Capital gains and losses must be separated according to how long the taxpayer held or owned the property. To determine how long property has been held or owned, begin counting on the date after the day the property was acquired and include the date of disposition." 

Short-term One year or less.   Long-term More than one year.