A US blade-type outlet will not have a very good (high surface contact) connection with a round connector (e.g. 12 or 14 gauge wire). Also, anything plugged into an outlet is considered a "cord". Any cord with an outlet on the other end is considered an "extension cord". It is specifically against the code to have extension cords within walls or passing through walls.There are sites dedicated to redneck electrical installations, such as this one: http://www.electriciantalk.com/f2/redneck-wiring-pics-39609/
However, getting back to that installation, which seems to have been done when a layer of insulation was added to the home (?), there seem to be missing grounds. If it was a repair, were grounds required? Moreover, while it does look bad, is that approach actually against code or unsafe? In other words, is it against code to plug one receptacle into another?
One can easily find 2-to-6 and even 1-to-6 wall adapters that do exactly that and have all sort of certifications, including UL and CSA. Maybe it was an attempt to avoid the problems of extending knob and tube (2-wire) wiring to accommodate a thicker wall that was just poorly executed?
Not to be misunderstood, I would not do it that way in my own home.