This experiment may be a case of having optimized for the capture of diffuse light. I think that the "natural" arrangement of solar panels would be only better if diffuse light was dominant over direct light. Multiple commenters have noted that trees were obscuring the flat array. We can presume that the location of the experiment had a limited amount of direct light. Also, a higher proportion of diffuse light during the morning and evening could explain the longer time periods of energy production.
If this hypothesis is revealed to be true, that could mean that this "natural" arrangement of solar panels may be optimal in situations where there is only indirect light available, such as interiors. Otherwise, I stay confident that the current knowledge about the placement of solar panel still holds.
Top Ten Things Overheard At The ANSI C Draft Committee Meetings: (5) All right, who's the wiseguy who stuck this trigraph stuff in here?