OneDrive is a client and api grafted on top of sharepoint. It's all sharepoint under the hood. You also dont need to use OneDrive to sync SharePoint, you can

OneDrive is a client and api grafted on top of sharepoint. It's all sharepoint under the hood. You also dont need to use OneDrive to sync SharePoint, you can use the File > Open menu to open in Word, Excel, PowerPoint to open files directly.