If you play, practice or coach during the season (even male players for women't teams) then it counts as a year. So the coach was correct. Here are the various rules from the handbook (https://web3.ncaa.org/lsdbi/reports/getReport/90011):
14.02.9 Participation in Intercollegiate Athletics. Participation in intercollegiate athletics occurs when a student-athlete either practices in a sport (see Bylaw 17.02.1.1) or competes in a sport, as defined in Bylaw 14.02.6. Eligibility rules for competition may differ from those for practice.
14.1.10 Male Practice Player Eligibility. A male student who practices with a women's team is considered to be a student-athlete in that women's sport. . . .See Bylaw 14.2.4.8 for use of a season of participation and
Bylaw 16.8.1.4 for benefits that a male practice player may receive. [I'd assume this also applies to the autistic example]
14.2 Seasons of Participation: 10-Semester/15-Quarter Rule. A student-athlete shall not engage in more than four seasons of intercollegiate participation in any one sport (see Bylaw 14.2.4.1).
14.2.4 Criteria for Determining Season of Eligibility.
14.2.4.1 Minimum Amount of Participation. A season of intercollegiate participation shall be counted in the student-athlete's sport when a student-athlete participates (practices or competes) during or after the first contest in the traditional segment following the student-athlete's initial participation of that academic year at that institution or when the student-athlete engages in intercollegiate competition during the nontraditional segment in that sport. This provision is applicable to intercollegiate athletics participation (practice or competition) conducted by a Division III collegiate institution at the varsity, junior varsity or freshman team level.
14.2.4.1.1 Exceptions. A season of participation shall not be counted:
(a) During the traditional segment when a student-athlete participates in a preseason scrimmage or preseason exhibition conducted before the first contest following the student-athlete's initial participation of that academic year at that institution;
(b) During the traditional segment when a student-athlete participates in an alumni contest conducted before the first regular-season contest following the student-athlete's initial participation of that academic year at that institution;
(c) In baseball, field hockey, lacrosse, soccer, softball and volleyball, when a student-athlete participates (practices or competes) during the nontraditional segment.
14.2.4.1.3 Student Managers and Student Coaches. A season of participation shall be counted when a student manager or student coach participates as a team member in practice or other physical activities during the time frame set forth in Bylaw 14.2.4.1. A student coach or student manager's role should be limited to performing traditional
coaching or managerial duties.