SQL Network Name owned by Available Storage OwnerGroup in Server 2012 FCI
It looks like a rogue client access point was added or someone manually moved/changed something.

Your two instances are as such:

SQL Server (I2)              Online                        SQL Server (I2)
SQL Server (I1)             Online                        SQL Server (I1)


They have corresponding network names in the proper groups:

SQL Network Name (clsnwname... Online                        SQL Server (I1)
SQL Network Name (clsnwname2... Online                        SQL Server (I2)


Each client access point also has at least one online IP:

SQL IP Address 1 (clsnwname... Online                        SQL Server (I1)
SQL IP Address 1 (clsnwname2... Online                        SQL Server (I2)


The outlier (failed) client access point:

SQL Network Name (I1)       Failed                        Available Storage 


Which you've stated isn't part of any of the SQL Resource Groups, isn't online (failed) doesn't have an IP associated with it (as far as we can tell from your output).

This leads me to believe:


Someone attempted to make this and didn't know what they were doing
Incorrect automated setup was run (with DSC, powershell, or other tooling [chef, puppet,etc])
Testing was done and not cleaned up properly


I doubt it was malicious. In any event, check out the dependency report - which I'm guessing will be blank. If it is, feel free to remove it and the associated computer object in AD. If it isn't blank, update the post with more information please.