I don't really like that explanation either because, as they state in this OP document, each report has to be looked at individually because they are all actual

I don't really like that explanation either because, as they state in this OP document, each report has to be looked at individually because they are all actually different. He says "these objects" as if the reports are all the same and explainable by the same thing. It is possible a handful of them are actually experimental aircraft (judging by their inclusion of that as one possible explanation for some incidents in the report and their statement that the reports disproportionately come from the area around DoD testing facilities, it's plausible), but that doesn't mean all the reports are examples of that, or even that a significant number of them are.