Hello Hassib
There are several things going on here. The first is that the output being shown is only for OSPF due to the ospf keyword used at the end. So you only see the OSPF routes, but the information in that particular line, refers also to routes that don’t appear. If you were to not use the ospf keyword, the output would look something like this:
172.16.0.0/16 is variably subnetted, 4 subnets, 2 masks
C 172.16.123.0/24 is directly connected, Tunnel0
L 172.16.123.2/32 is directly connected, Tunnel0
O 172.16.123.1/32 [110/1000] via 172.16.123.1, 00:01:23, Tunnel0
O 172.16.123.3/32 [110/2000] via 172.16.123.1, 00:01:13, Tunnel0
Note, for reference, that the output is for Spoke1 of the lesson, same as your output too.
So here you see that there are indeed 4 subnets, because directly connected networks appear as two separate subnets, one for the whole subnet and one for the particular /32 address. Note also that there are two different sizes of masks. A /24 mask and three /32 masks.
I hope this has been helpful!
Laz