There are two functions which read a VM metadata on Kimchi: libvirt_get_kimchi_metadata_node (the one you changed) and _kimchi_get_metadata_node. Both functions do the same thing but in different ways: libvirt_get_kimchi_metadata_node uses the libvirt metadata API to fetch the metadata info from a VM (= easier to use), and _kimchi_get_metadata_node reads the metadata info from the VM's XML (= harder to use). As you can see in get_metadata_node, the first function is called when the host system uses a newer version of Kimchi which supports the metadata API, and the second function is used otherwise.
Your patch is changing libvirt_get_kimchi_metadata_node so it parses the XML _and_ uses the metadata API to get the metadata info. If we want to avoid using the metadata API (because it always prints messages when a VM has no metadata, which is what this issue is about) we should then use the function _kimchi_get_metadata_node every time.
Also, we always use the Python lxml API to read XML data. We used to have mixed APIs in the past and it was hard to maintain, so we decided to use the same one in order to keep consistency.