You can tell we are of earth because we're fecking morons thinking nuclear weapons are special.
Any beings capable of travelling from other galaxies to us have harnessed forms of energy that we've probably not yet even discovered.
Arguments of the form: "This speculated motive/cause doesn't make sense, therefore the observation that inspired it is false" are fallacious.
The observation is the observation. Should we dismiss it simply because a speculative motive/cause for it seems ridiculous? No. To get at the truth, we need to first figure out whether the observation is true or false, and only if true worry about motives/causes. Arguing the other way is begging the question.
Reminds me of the trouble scientists had accepting the reality of meteorites a couple of centuries ago: Newtonian laws are 'perfect', there are no rocks/iron chunks in space and therefore the observation of falling rocks/iron chunks by 'illiterate peasants' - who were apparently the only ones who observed such things - cannot be true. Never mind that the Romans, etc. wrote about them (dismissed as superstition as they also wrote about blood, etc. falling out of the sky). Yet it was right there! If some brave scientist had overcome the social stigma to investigate the truth/falsity of the observation first, they might have found themselves on the road to understanding Solar System formation much, much earlier.
BTW, anything that can convert mass into energy directly, and deliver that quickly and to a small volume, however crudely, is no joke. Whatever your level of technology. cee-squared doesn't play. That weapon represents something about us, good and bad.
And who says NHI are from other galaxies anyway (billions of stars in the Milky Way alone)? Are they even extraterrestrial/alien?
Speculations:
It's less about the weapons themselves than about what these weapons signify (to us). E.g. Prof. Bob Jacobs' account of the Vandenberg AFB missile incident suggests NHI are demonstrating overwhelming superiority and control. Are these weapons your state-of-the-art? LOLZ. We can knock them out of the sky, or (de-)activate them at will across thick, shielded concrete. Bet you can't even figure out how we did it, can you? Ditto the Nimitz encounters: we can come and go as we please, do what we need to do right in the middle of your AO, and there's sweet feck all you can do to stop it. And hey! That uber-secured, super-duper secret CAP point of yours? Yeah, we know where that is too. Just watch me zip there after you tried to interdict me. Can your fancy jet even keep up? LOLZ.
I also strongly suspect we are mere nuisances NHI have to deal with - or keep an eye on - once in a while as they pursue their true purpose. They've probably been here, or 'nearby', a long, long time. And while they appear to have unrestricted range (undersea, land, air, space), we certainly don't. So our observations of them occur only within a limited set of possible scenarios. Which means said observations are not necessarily representative of the true scope and nature of NHI activities. Our observations are biased by our limitations and NHI posture toward us within those limitations.
NHI: 'Non-Human Intelligence'; because 'alien' implies extraterrestrial (from another planet in this or other solar system). That's an extra assumption.