Well I would say that would not be all that uncommon for people with a lot of money, as much as they apparently have, to keep such a large amount of cash at home.
A 'sane' reason to keep that much money at home would be for bitcoin trading purposes, as it would probably be a bit of a hassle to have to go to the bank every time burt wanted to buy or sell large amounts of bitcoin, plus the fact that making a lot of cash deposits and withdrawals out of a personal account (he wouldn't have a business account because he was only doing it as a 'hobby') is a good way to get your bank account closed.
I am not sure what exactly Burt's wife's company does, not what the client does. Both the businesses names were redacted (and the locations

) in a letter that she wrote and published in a different section on her site. I would say there is a good chance that it would be difficult/impossible to determine exactly what they do.
I understand not using banks. I grew up next to the wholesale fresh-cut flower market that was open 4am-7am, for the delivery at 8am-9am, which was also before the bank hours. I think I mostly understand people dealing "cash only" and having suitcases full of them. But never at home! This is dangerous, you paint a target sign for yourself and the family. And I'm not taking about "jackbooted government flunkeys", just a regular old-fashioned violent crime. Neither BurtW nor his wife seem like random naives or Bitcoin cultists/evangelists.