After realizing no one was around to fill up his beer, this customer took things into his own hands.
Usually, when you're at a restaurant, the server is readily around to help you. That's whether they're coming by to take your order, check on you, or if they're just in the vicinity and can be flagged down.
For people with drinking as a priority, they'll even cut out the server and just sit at the bar. Here, they know they'll be well attended to since their server/bartender is right behind the counter.