I've worked with guys where socialising, especially as they start out on their careers, was part of the job. However, every single penny spent was expensed.
Getting that drunk was never expected though - to be honest, if it was a long term situation, I would have thought it would be frowned upon, even among their friends. (Their work contacts often ended up being friends as they spent so much time together and it guaranteed business.) (I worked in Finance - they do NOT pay for it themselves if part of the job.)
I think your husband is a functioning alcoholic (or scarily close), and that deep down he knows this "work" story is nonsense, which is why he is now hiding the receipts.
If I really had to give him the benefit of the doubt re work, he could stop drinking when out for a couple of weeks, saying he is on antibiotics. And then switch to water or coke etc. Or he could just be an adult and say he's cutting down when asked.
I really feel for you, as I think he doesn't want to be helped, and I don't know what way out there is for you if that's the case. But in answer to your OP - he's bullshitting. Sorry.