Well, I got what I wanted by using a Player Attribute instead of a pawn's attribute, but I still don't understand where that 774963301 came from. What is interesting is that it always returned that number, until I tried a different pawn/attribute. Then it generated a new number (still nine digits long) which was always the same for that pawn... ? Only the Player Attribute gives exactly what I want (i.e. a 1 or a 0).
I've had that problem too... really weird numbers come when using the SetAttribute/GetAttribute commands. I tried to get pawns to check what kind of projectile hit them by using different attributes but it didn't work out ...
It seems that you can add multiple attributes with the AttributeOrder() command ... but only only the last attribute acts as the health attribute. However, I managed to build a detection system for different kinds of projectiles.
But hey... if someone has got those AddAttribute/SetAttribute/GetAttribute commands working, please inform us.