When i get attacked, sometimes when it lists the units that were expended in the attack the Clan Shield of the clan the attacker was in at the time of the attack appears, when i review the attack i see this stone with the Shield above it placed down and units come out of it.
Is this stone in some way linked to the user's Clan Castle?
Yes, this "tiny castle" is in fact linked to their Clan Castle.
When in a clan, you can request troops from your clanmates. If you have troops in your clan castle, they will automatically defend your base if it is attacked and the attacking troops enter the clan castle's radius.
Alternatively, you can deploy these troops to bolster your own forces during a raid. They will show up in the troop selection bar with an icon denoting your clan's shield. Deploying them is an all-or-nothing affair.
Either of these two things will use up the troops in your clan castle.
