It wasn't deemed signed, it was deemed acceptance. In English-derived common law system, a written, signed agreement is required for certain special contracts, but the normal requirement is offer and acceptance of an agreement with consideration, writing and signatures are evidence of content and acceptance, but not generally required for it.
Thanks for sharing - I didn't know this was not a new situation for the law, but it makes sense that many contract agreements find themselves moving forward without a real signature.
