Didn't see this one personally (I'm over in Liverpool so a bit far out of range!) but this has got me genuinely curious. A few things I'd want to know before drawing any conclusions:
Were the lights equidistant from each other, or did the triangle shape shift at all during the sighting?, Any sound reported? The silent/near-silent aspect tends to be one of the more consistent details in credible UAP reports, What was the approximate altitude - were we talking commercial flight height or much lower?
The reason I'm asking is I've been cross-referencing a load of Great Lakes sightings from the past 18 months using MUFON's case database and there's a noticeable cluster of triangular formation reports specifically around that region. Not all of them hold up under scrutiny but some of the witness accounts are remarkably consistent with each other despite coming from people who clearly hadn't compared notes.
Did anyone manage to capture footage? Even shaky phone video is worth analysing - I use Avisynth for frame-by-frame breakdowns and you'd be amazed what gets missed at normal playback speed.
Also worth checking whether there was any unusual weather activity that night. Lake Michigan has some odd atmospheric conditions that can produce convincing light anomalies, so it's worth ruling that out before going further. What's the rough timestamp on this?