While I find it highly unlikely, it does raise an interesting point about Fermi's Paradox, which is that even if there were enough alien life out there for its discarded light sails to go hurtling through our solar system every once in a while, we might not get any more evidence of it than this article demonstrates. So, it's almost certainly not a light sail, but even if it were, we would never know.
Fermi's paradox demonstrates it's almost certainly not a light sail. For it to be a light sail which was observed by chance by our totally unprepared observatories after a window of less than a century but also consistent with all our observations of the universe, we would need to hypothesize that we got extraordinarily lucky to observe a super-rare artifact, or that countless (or one vast) interstellar, pan-galactic…
I'm fairly certain we can't detect that yet even if they had.