I can't speak to whether Google Maps was listening at all, but you can verify whether it is by opening Google Maps at home on your wifi network, and inspecting the traffic using something like Wireshark.
What's more likely to have happened is just having a crap ton of data about you and your friends.
Here's how it might go down: You and each of your friends own mobile devices, and each of those mobile devices has Google Maps on it, presumably. Apple or Samsung or Google or whoever made your phone is collecting telemetry -- it knows your location at all times. Your device is assigned a unique, anonymous ID, and all telemetry about your phone is being sent on a regular basis to headquarters. Things like your latitude/longitude, how long the phone has been open, what apps you're opening or not opening. Whether you realize it or not, your phone is basically telling on you every time you do it. It's typically anonymized data, but it's still tracking you.
I should add this is happening on your desktop and iPad and iPhone and even your work computers. Facebook knows who you are, regardless of which device you signed in on, and they remember that information. So does Google, Target, Amazon, Etsy, and probably even IRS.gov.
AppAmaGooSoft and every other app telemetry company is buying and selling data from each other, so they can cross reference it. They know that your wife is pregnant, because User X16AF has been to the lat/lng coordinates of the hospital at certain times, and because Target reports that User 99AFJJ1 bought a pregnancy test three weeks prior, and the device hardware ID was in very close proximity to both of those actions, and by the way, they know it's your wife (or family member) because your device is in the same house as her device for 14 hours per day.
That's a fairly obvious scenario. And from there, it's easy to see that you or one of your friends must have read something about this local attraction. Did they read an article on the local news website? Did they see an ad on FB or Instagram or Twitter or TikTok? Did they make a search in Google or Bing? Did they check it out on Google Maps?
Things like "hey, we should check out X Attraction" don't spontaneously appear in people's minds. They got that information from _somewhere_, and most likely, that _somewhere_ is tracking you _somehow_, and that's getting correlated with everything else everyone else knows about you, and Google eventually says "User YQ196C saw an ad about the Local Ax Murderer Convention on Facebook, and our Google Maps app says that YQ196C is in the same car as User PI815ZB, and we know the app is open, and they are both within 15 minutes of the Local Ax Murderer Convention. Let's pop up a message to see if they want to go." It could have been hours or days or weeks ago that one of you saw something about that convention -- maybe multiple of you did! Who knows?
There are people here who know a heck of a lot more about this than I do, and I'm sure I'm overly simplifying and overly complicating certain aspects of this. But I do know that we are all being tracked (albeit mostly anonymously) and that Google doesn't know that it's YOU, Karl Gluck, but they know that your device correlates to a heck of a lot of activity around the world, and that's how they target ads at you.
I don't see this as particularly nefarious. Nobody is "spying" on you, in the sense that they're listening to the things you say and reacting to it in real time. Instead, they're correlating vast amounts of data about vast numbers of people and drawing some conclusions that are probably mostly wrong -- you don't think about these ad attempts that aren't relevant to you -- but are surprising and mildly disturbing when they are correct!
As far as I'm concerned? Privacy is dead. But at the same time, nobody cares about you, Karl Gluck, or me, Jemaclus, specifically. Nobody, not even an algorithm, is sitting there tracking you or me specifically. It's all about aggregating huge amounts of data and drawing conclusions about data points that overlap.
Not sure if this will give you nightmares or help you sleep in peace. But either way, I think you can rest assured that Google Maps isn't "listening" to you in the sense that your post implied.