Yeah even if Ruby is not much younger than Python, it only gained popularity outside of Japan somewhere around 2003, and only extreme popularity after the release of rails.

I always wondered how dhh came into contact with this unknown language

I was using Ruby regularly circa 2001. It wasn't unknown in the West, as various magazines had pointed out this neat Smalltalk-like scripting language and the first version of the Pickaxe book was also published in 2001.

It was not that unknown, there were definitely people using it in the west before rails was released. It was just not in the mainstream consciousness.