Good overview. The warning signs were there before the earnings announcement. I just pulled together a buy:sell chart of Retail Sector (using SPDR Retail ETF XRT) and Walmart. This shows Walmart outperforming its sector until January 2018. The turnover was confirmed about a month ago. XRT is an equal weighted ETF - Walmart is in there but only about 1.5% of the total fund.
Now I am tempted by the 10% drop in price for a different reason. Walmart has an amazing network of stores across the country. They can leverage these as distribution hubs for an offline/online business to overtake Amazon's delivery promise. My understanding is they are working on it.
Walmart has the free cash flow to attack Amazon, just not sure about the management team. I agreed with the chart you pictured above, the drop was coming and the earnings release was just a timing mechanism.