You need to be careful with this strategy as you can end up in waiting a long time with your money "out of the game" and it is depreciating in value all that time. Inflation will erode the value of your money, so you need to have it invested or in high earning savings accounts to offset the loss in value. You will also not be alone in bargain hunting during the bad times and people with considerably deeper pockets will have a lot more in reserve to outbid you. There may be less competition from the average person because they'll be unable to take loans, so you will have a slight advantage there.
I do think he's wrong for thinking in this way, war and crisis shouldn't be something we should be praying for because it hurts alot of family and we might lose ours too because of this hard times. Buying land and properties during crisis can be a risky investment as you don't know what's going to happen after the crisis. Attention shift from one type to investment to another during economical crisis. After the great collapse of the economy in 2008 that's when Satoshi decided to create Bitcoin in 2009 and those that invested have made some for the best decision of their life. During crisis, new and improvement things to invest into comes out hence, you thinking that you're making the right decision by investing in the old things you knew about before the crisis can make your investments to be a wrong one.