Have you noticed that there are additional files with extension dtsx.designer in your Integration Services 2016 projects?
You are 100% sure that you did not create a file like that and also, it can be opened; it is an XML file. If you analyze the file, you should notice that it is similar to your dtsx file but has additional nodes.
As you see, dtsx.designer has more nodes though the content is similar. This file is automatically created when you use one or more Package Parts in your package. This is one of the new features introduced with SQL Server Integration Services 2016.
Note that this file is used only at the design-time. At the run-time, it package parts are getting added to your original package (in my case LoadProducts).
For more info on this, read: https://msdn.microsoft.com/en-us/library/mt620034.aspx