Medieval people certainly believed that. The linked wikipedia page does not say otherwise. It states that "European scholars and educated people during the Middle Ages believed the Earth to be flat". Most people in Medieval times were not scholars or educated. Furthermore I haven't even said anything about Medieval times.

There are other examples like rocks falling from the sky or the earth- or solar-centric cosmos, if you prefer.

That Wikipedia page can be edited by any visitor, therefore it is not a reliable authority on the posted information. Take a look at the revision history page for your link, https://en.wikipedia.org/w/index.php?title=Myth_of_the_flat_.... Half of the edits appear not to be attributed to people but to unnamed ip addresses.

i.e. Don't believe everything you read.

To illustrate this point, go to different Wikipedia page that shows the opposite of what you wrote, https://en.wikipedia.org/wiki/Flat_Earth and look at the Early Middle Ages of Europe, https://en.wikipedia.org/wiki/Flat_Earth#Europe:_Early_Middl....