Hello Rodrigo
Just so you know, I edited your post so that the config and the NTP associates table appears correctly, otherwise the columns were off and it was very difficult to read. 
You are correct that the software clock will be synchronized with NTP so it doesn’t really matter what the hardware clock says. The purpose of the hardware clock is to be a source of time synchronization when the device is rebooted. Using an internal battery, the hardware clock gives the initial time to the software clock after bootup. It’s a good idea however to make sure that the hardware clock is synchronized. This will keep a level of time accuracy in the event of a reboot and a loss of connectivity to the NTP server, as unlikely as such events occurring simultaneously may be.
You can configure the hardware clock to be periodically updated using NTP just to be sure that synchronization will be maintained even after a reboot. For more info about this, take a look at the following Cisco documentation:
As for your second question, the clock synchronization algorithm used by NTP and the process by which it chooses the time source it will use can become quite complex.
If you want to get into the details of the sync algorithm take a look at this link: (I don’t usually post Wikipedia articles, but this is well done so there you go.) It’s more detail than you need for certification but it’s interesting and can be helpful to know.
Now during the execution of the algorithm, all of the NTP sources are examined, until up to three candidate sources remain. (This is what the “+” means in the output, that this server, in the running of the NTP algorithm, was a final candidate.) From those, based on various parameters such as delay, latency, and offset.
Keep in mind that the stratum number represents the distance from the reference clock and is used to prevent cyclical dependencies in the hierarchy. Stratum is not always an indication of quality or reliability and it is common to find that you may have a stratum 7 source preferred over a stratum 6 source, as is the case with your network.
So your result is not in error, but is based on various parameters beyond just the stratum.
I hope this has been helpful!
Laz