That's the most common cause of a crack around the area of the "freeze" plugs- - - -which, BTW, aren't intended for freeze protection. The holes are there so the foundry can knock the casting sand out of the cooling passages after casting the block, then the holes are machined to accept steel or brass plugs. They are actually known as "core plugs". Sometimes the plugs push out when the coolant freezes instead of the block cracking, but it's not guaranteed by any means. The nice thing about an external crack is that it doesn't have to seal compression or combustion pressures. A patch that can stand cooling system pressure without leaking is much simpler to do than fixing a cylinder head or cylinder wall crack.
It's also possible to have an internal cooling system crack that puts coolant into the crankcase, but it's not as common as getting damage to the outside of the block.
Jerry
