Very likely it is due to the fact that the absence that triggered the Infraction was a Pre-recorded Absence. When the date of the Pre-recorded absence is reached, the name of a user who has the Schedule Manager role is selected to be the one listed in the database as the one recording the absence. This is done automatically behind the scenes and cannot be changed.
In the Conduct module, the user who recorded the absence that triggered the Infraction is listed as the Author of the absence Infraction on the Lists > Infractions page. Therefore, in this case, the "Author" likely has the Schedule Manager role, or did at the time the absence Infraction was assigned.