Excel 2007 and forward is stored as a zip file containing XML files, the code you showed above is XML, and the error you showed is an XML error. So, yes, it's an XML file even if it looks like an Excel file to you.
Can you paste more of the file? The error is a very simple one. It means that an XML tag has multiple parameters where a space is expected to separate parameters. For example, this is the workbook.xml file from a simple Excel file. Do you see the places where I've put a red X? Those are examples of where a space is required. If the space is missing, you will get an XML parse error. I have never gotten an XML error trying to open an Excel file. It suggests that some software other than Excel may be creating the file and has a bug. It seems very unlikely that this could be user error if you have not tried to edit the XML, and from your response I would say you haven't.
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