(I have no idea what happened in this case, and I'm not saying a spoken agreement is necessarily a contract or that you definitely can offer any given piece of evidence to prove it. The rules are complicated. But contract law is basically about fairness, not technicalities. If "you have no legal proof!" sounds unfair, that's a good hint that it's probably not an accurate statement of the law.)
Just because the idea is kind of neat: It's possible you're getting jumped on by the lawyers here because "legal proof" itself is such a non-legal concept. There's such a thing as mathematical proof, for sure. There might be such a thing as scientific proof. But you could rarely point at something and say "that's legal proof." You could only say, "that turned out to be enough evidence to convince that particular jury." "Proof" is defined by the observer (jury, judge, etc.), not the object (contract, bloody knife, etc.).
He did have a contract. It just wasn't written and signed. It's still a contract. The CFO is misleadingly implying that because it was not signed, there was no contract.
The mere fact he has the email exchange which took place between them afterwards is probably enough evidence to show in court that a [contractual] agreement existed. Miso was dumb to ever respond. They would have been better to pretend they never saw or heard from the gentleman again and leave it to him to sue... with little to no evidence that the agreement existed. That still doesn't mean Miso doesn't suck... it's just the move Miso should have made if they were going to try and be dicks about it, like they were. Miso, should have just paid up right away, they got caught red handed though and their legal counsel probably said... pay up, it'll save you as much or more and cause you less legal headaches and stress... let's just make this go away and save ourselves from losing focus on a legal fight we will probably lose and minimally will cost as much or more to fight.
It's easy to pretend you didn't get an email. But what if you send via registered post a letter, or a courier? What do you do if the employee has a signed form saying you received the letter? Blatantly ignoring the good faith attempts to resolve this matter before courts are involved might harm your case.
That, and because verbal contracts are not enforceable for all transactions.
Oh, they definitely sue over verbal contracts all the time. Just trying watching any of the dozen Judge X shows on TV or visiting a small claims court. Indeed, the reason for small claims courts is largely to keep these types of disputes out of real courtrooms.