This is not the correct behavior in my mind. It should behave the same way as if the page was created via the OneNote client. This behavior creates a big usability issue for our end users since the whole page will be covered with the green color of changes in the page.
Request
POST
graph.microsoft.com/v1.0/groups/{groupid}/onenote/sections/{sectionid}/pages
HTTP/1.1
Content-Type: text/html
Response
HTTP/1.1 201 Created
request-id, client-request-id
Screenshot of the OneNote client