GE built DWs during the early 1950s that were designed to be dropped into your counter top, it was basically the same DW that was also part of the DW-sink units, so this is a correct and proper installation.
John, you are 100% correct. The stenciled date is May 1950. In addition to the freestanding and electric sink versions, these drop-in models were also available. Likely, it is a Model AE-100.
This is the very first drop-in GE Dishwasher that I have seen advertised on Craigslist (or other online sale).