This is probably one of those deals where something was left out of the 2nd sale. I have seen homes on say 5 acres that sold, and again in the next few months sold again for less money, and less Land. In this case if the home on 1 acre sold the 2nd time, the old owner got 4 acres for much less than if they had purchased just the acres. I know of a lot of deals where dad wants the land, and son or daughter wanted the house, so dad purchased all of it and sold the land or the house to a child. There is NOTHING wrong with either sale of this property. (Get the Facts)
You have to look at the deal and find out What was sold.
As far as an Auction Sale, these are normally a "Cash" value - (As Is- Where Is) without any stipulations. The Auction is the Real Deal without any Fluff from special financing, repairs needed and an NON Refundable Deposit that separates the Liars from the Buyers. That is why an Auction may appear to be less money. I reality, it is the real value of a property, when properly advertised and promoted. At the same time the Seller knows WHEN the property will Sell and WHEN they get their Money! Most of the time, it takes a total time of 45 days. (Auction Listing-Promoting-Advertising-Auction Preview-Auction Day-Closing)= CASH
You also don't mention how much lower of a price - significant or just "lower" - and what's the price point/area? Without pulling detailed information it's impossible to say here.
As a broker/appraiser, when I see that type of sales history, it can be a "flag" that the 1st sale was a foreclosure/auction sale by the bank. The second sale many times (but not all) is when the bank sells the home on the open market. Certainly there can be other explanations; one would have to look at public records to see the names of the sellers. Hope that is helpful in your search for an explanation....