Maybe the establishment has a BTCPayServer or it may be using Swiss Bitcoin Pay, if there are bitcoin gateways that allow payment for the products you have, you can set up a store, point of sale terminals among other things. Maybe it was a normal payment. You consume 50 usd, I come with my wallet and I create an invoice for that amount. The first applications that I mentioned have the advantage of accounting for the operations and keeping track, they are made for that.