No, it just wasn't dark yet. Yeah, light pollution sucks, but you could tell it wasn't truly dark by the fact that it was noticeably darker after the fireworks were over than when they began. Just looked it up and "nautical twilight" began around 10:40, and "astronomical twilight" at 11:40 pm.
I'm surprised by that, as I live a good way north of most of the USA, in London.
I looked up Macinaw City (since I've been there): sunrise is 05:54, sunset 21:32, solar noon 13:43. Accounting for DST, that's 43 minutes "off".
In London, solar noon is at 13:05 (we are also on DST), sunrise 04:50, sunset 21:20. Almost an hour's extra daylight. (And no astronomical twilight at all until 22 July.)
The local Americans (quite a big group, there's an "international" school not far away) had their fireworks at 21:30, for some odd reason.