Yikes, that's scary and points right to your question. Older homes rarely had GFCI outlets installed, especially outdoors where they're most needed. Have you checked if your own outdoor plugs are protected?
Ugh, that reminds me of what happened to my friend Kyle. His back porch outlet completely melted after a storm, same deal. When the inspector came, he pointed out the old wiring and said, like sandrahayes mentioned, there was no GFCI at all. They had to redo the whole circuit. It was a huge pain and cost way more than just putting in a protected outlet years before.