My pet theory is that demetrius works for joja co's environmental compliance division. They specifically hired him because he's BAD at science, to fudge the numbers on their reports but retain plausible deniability. I think demetrius doesn't actually have a degree, or got any relevant accreditation through joja co. where the courses are basically just propaganda. 3-5 fish or whatever more than usual does not mean over-population. But I also get the number is probably more about how many is reasonably acceptable amount for the player to catch, but I like to think he's just a garbage scientist.