Hello Giovanni
The question has to do with the specific flags that are outputted by this command. Each flag has a different meaning. You can see the meaning of each one at the following command reference:
According to this command reference for the unique flag, "This flag indicates that an NHRP mapping entry cannot be overwritten by a mapping entry that has the same IP address and a different NBMA address.
Similarly, it is the implicit flag that “Indicates that the local node learned about the NHRP mapping entries from the source mapping information of an NHRP resolution request received by the local router, or from an NHRP resolution packet being forwarded through the local router.”
In the output, there is a unique flag, but no implicit flag, thus the first answer is correct and not the second.
Both Phase 2 and Phase 3 enable directly spoke to spoke communication, however, they do so in different ways. The difference is in how NHRP operates. Take a look at the explanation of both Phase 2 and Phase 3 in the following lesson:
I hope this has been helpful!
Laz