Extraordinary claims required extraordinary evidence. A massive rock being hurled to by a supernova to our solar system is far more likely than advanced aliens dumping a ton of future tech to get this huge thing into our solar system for a split second.
Why? Because, it would cost a lot of energy, something I doubt an advanced race would spend. Further, an advanced race that wants to probe us wouldn't need such a huge object, it's far easier to observe from a far (think, james webb telescope but better). Sure, hard to know what aliens are thinking, but it just seems incredibly unlikely they are thinking "Let's build this half mile long space probe for a glimpse of a distant solar system and send it off for a million year journey".
A star exploding and sending a bunch of mass our direction is far more likely. Why? because we know that happens relatively frequently.
While I agree with your overall conclusion, I don't see that we have any evidence that as a race progresses technologically, they spend less energy. The opposite seems to be true.
The problem with "can't disprove" being used as evidence is that you need to consider the full universe of statements that we "can't disprove", but humans tend to think as if "alien probe" is a privileged statement simply because it is cognitively appealing and drives our imagination. If you put it on a list of the things we can't disprove about this particular object, it wouldn't really be the most likely one you'd find.
On the flip side, you also ought to consider the question of all the objects for which we can't disprove they are alien probes. It isn't just this particular object; the solar system is filled with millions of objects we can't disprove are alien space probes, things we've labelled as "asteroids" based on a streak someone took a picture of once. Apply the same standard to all of them that is applied to this object; does it now claim that the solar system is just filled to the brim with alien space probes? Probably not good logic.
Personally, I can't wait until we improve our detection a bit and detect another several dozen things like this object so we can get over this and real science stories can be written about these objects again. Guess this is a taste of what reading about pulsars must have been in the first few years.
This is a good reason enough for some people to write a book for a general audience!
Thanks!
Will that do? I also have some whole wheat bread that my kids say taste like dirt.