How so? My main complaint is that text that is part of flash content can't be resized. How would that happen if they used HTML5 instead?
Also, the restaurant owner is likely a non-technical person, who probably doesn't know what features are possible with what format. How do I know that they didn't just say, "We want a nice looking website, and we want it to present our menu, here's our menu." And the website designer decided to use flash to code the menu? I mean, I don't know if that's how it happened, or if you are right and the website owner asked that the menu be presented in flash, but is there any reason to assume one over the other?
Now, if the menu was truly interactive -- like let's say, you are able to click on different items in the menu, and as you click, it shows a running total of your order -- and you tell me that in order to do that, you had to use flash, fine, I'd understand. But no, the menu is just a static menu. In fact, it's just a scan of their printed menu. If the owner really asked that the scan be used on their website, and the designer didn't point out that the scan would look horrible on higher resolution monitors, then the designer did his client a real disservice.