[bmm6o]

I'm not sure if you're saying you're not familiar with the meaning that the word has had since the early 15th century, but http://dictionary.reference.com/browse/poaching?s=t. It's application to business employment is obviously much more recent - I can't find a definitive citation, but I'd be surprised if this usage even dated back to the early 20th century.

I find it an inapt analogy to describe a transaction in a competitive job market.