If there were 7 of these ripe for the plucking that were actual Dyson spheres, each one would be the single greatest discovery in all of humanity. Just seems a little too easy.
think of it this way: imagine in the future we travel to Alpha Centauri and find sentient life or even the remnants of such. That would be really bad. Why? Because if there are 2 civilizations in our galaxy, how likely is it that they're next to each other? Incredibly unlikely. It heavily implies that sentient life is much more common. Now imagine if we find a third at, say, Barnard's Star.
In Fermi Paradox terms this heavily implies that there is a Great Filter ahead of us and we're more likely doomed than not.
Finding a Dyson Swarm near us has the same negative implications (for us), especially given that the gap between a partial or full Dyson Swarm and colonizing the galaxy is relatively small (~100 million yaers) in cosmic terms so how likely is it that we find a Dyson Swarm that is a) near us and b) in that narrow window between the emergence of spacefaring life and colonizing the galaxy.
If we find abundant evidence of intelligent life, there is no fermi paradox, and thus there would be no reason to explain life's fictional rarity. The answer to "where are they?" is "right over there."
Suffice to say the 7 candidates in the article do not conclusively have another explanation. Hence their status as Dyson sphere candidates.
It's not saying we don't know what causes lightning therefore it must be gods. It's saying we have expectations of what lightning looks like and this looks a lot like it.
There is a significant distinction between "we've found a Dyson sphere" and "we've found an object that has the characteristics we would expect of a Dyson sphere".