The report does not suggest that its conclusions are “hard science”. It explains at the beginning that if there are common threads in social science research, then those common threads are more likely to be reliable. Social science never has the reliability of “hard science” because the experiments cannot be repeated. But in ordering human affairs, we have to rely on something, as imperfect as it may be. On p 252 the report quotes the John Jay data that shows that after altar girls were introduced in 1983 “the offending rates against both altar boys and altar girls were approximately equal (Terry & Freilich 2012).” That would suggest that opportunity is a much more important factor than sexual orientation. There is a whole subchapter on the John Jay reports and its findings (which the authors do not dispute) that most abuse was with post pubescent boys. They do disagree with some other aspects of the John Jay Reports, but not the ones you mention.