Apple's iPhone Health App does not collect data directly rather it is a repository of data accumulated from the Apple Watch, a variety of third party apps that in turn collect data from glucometers, sphygmomanometers, electronic scales, etc.
as well as accumulating and recoding health data from medical providers online patient "portals". Exercise metrics are generated from data and measurements taken by the Apple Watch and communicated to the Health app on the paired iPhone by Bluetooth. The watch data is in turn generated by actual pulse measurements, ECGs, as well as arm and body movement detected through multi-axis accelerometers. You need to tell the watch when you begin strenuous exercise to get accurate credit.
I don't know about calculating flights but various movement metrics are imputed from a combination of physical movements typically associated with a particular activity and the measured pulse rate all taken from the Apple Watch.
As to the data you sent to the iPhone an xml file is not readable by Excel or Numbers. Those apps can read .CSV (comma separated value) files or their own proprietary formats. This article
will explain what an XML file is and how to read them as well as a link to a site that will translate XML to CSV. NOTE:
be aware that is a Windows-centric site. However how you would get the csv data into the Health app I can't help you other than most of the data can be keyed in manually. ADDENDUM
Since XML is a first cousin to HTML (both are markup languages) some browsers can read XML files. I don't know if that includes Safari or not.