When I was in college, there was a 24-hour diner down the street from the main strip of bars. From midnight to 5AM, everything was significantly more expensive. They had two sets of menus with identical offerings but different prices and changed which ones they handed out, but were never too strict around the changeover times. If you showed up at 4:45AM and weren't drunk, they'd definitely give you the less-expensive menu.
This is basically happy hour. Though the app notification (why would I ever install a pub app?) feels like it could be a slippery slope to true dynamic pricing. Though revenue management for going to the pub seems like a poor use case.
That's just poor marketing. They want to _discount_ at non-peak hours. See? Doesn't that sound much better?