The second and third video doesn't mean anything either.
How would you program a sale of this sort? In some data source you would have the time period for the sale and the max number of units of each type of product to be allowed. On the client side UI, it makes sense to hide/show the sale button base on the client side time, but no sane programmer would rely on the client time for the actual transaction. So lets say the user gets the buttons enabled somehow before the sale starts and clicks it, the request goes to the server, but the server sees that there are no stocks to be allowed for sale during that time, so an error has to be returned. If the programmer wants to be specific, he can handle it specially and show the user a message that he is trying to purchase before the start time, but all that extra work doesn't make any sense unless you want to follow that up some action like say barring the user from the sale altogether for trying to cheat the system. The default and lazy approach any programmer would take is to show the default error which would be "out of stock".
There are a number of systems where I have seen this kind of default/lazy approach taken for errors of that kind.
In a popular online skill assessment system (I don't want to name which one) that is widely used in UK colleges and companies, the system has a time limit to answer each question. The timer shown to the user is running in the client side JavaScript and you can pause it quite easily by invoking an alert box via console or from address bar. You can take as much time as you want and no error would popup while going through the test. But the server also makes note of the time from question popup to when you answered it. So it knows when you didn't answer the question in time. At the end of the test, it won't tell you that you tried to cheat the test or anything. It will just mark the question as unanswered even if you put in the correct answer.