I do think this is a good possibility regarding the events taking place. As for the Annual April Fools Biking event, below are a couple links with details of the route and a trail map. Looks like the trail itself is 52 miles and spans between Hiawatha and Evansdale. The annual ride covers a portion of that between La Porte City and Brandon. There are also event pages including past rides and the most recent event which can be found on Facebook. Getaway Bar and Grill located at 106 Commercial St. is a place noted on the event page. The person hosting the event page did state that they were contacted by the FBI to request riders to submit their digital media from April 7th. The link for this page is also below. Figured it would be ok to post it since it's not a personal page but instead a public event page.
This year was the 16th year for the ride and it seems the same route is used every year. I imagine there are also traditional stops and activities that take place. Someone with sinister intentions could definitely use that knowledge to their benefit though I truly hope that isn't the case. I have lived in Iowa for 16 years. We have so many trails and biking events in Iowa but I had not heard of this one specifically, though I am not really into cycling either. I don't know how far an avid cycler would travel to partake in these type of events.
I did also find out that even my community has one of these Annual April Fools bike rides, but recently was cancelled for snow and ice storm. So now I wonder if this specific event takes place in several Iowa communities and if others have went missing in past events around these same dates.
If someone did take advantage of this event they must at least know the area pretty well including what type of security measures are in place in the community and for the event. They would also need to feel comfortable as far as blending in. Not saying that this would be someone from that area specifically but perhaps attends these events frequently.
https://www.traveliowa.com/getinspireddetails/iowa-biking-bucket-list--the-must-ride-events/152/
http://trails-web.devface.com/index.html#api_key=INHF&id=103
https://www.facebook.com/events/203958596819152