There's no other reason I'm aware of.... It was dry, I could hear that much!
What do you think the cause could have been?
A poorly lubricated chain causes wear directly on the pin and only on one side of the pin. When the chain is at the end of its life, that pin (which is 3.5mm thick) shows wear of only 0.02mm.
To wear through the pin until it is thin enough to break is inconceivable. The chain stops engaging with the sprockets long, long before wear is even in the 0.5mm range.
Therefore the pin is not weakened by chain wear.
Your chain didn't break because the pin was broken in half, it broke because the pin's peened head was forced out of it's seat in the sideplate. Most likely from poor shifting. It is easy to break a chain by bending it sideways but no-one, not even Chuck Norris can break a chain in tension (direct straight-forward pulling).