The sales volume is based off of the number of seats in the establishment, not the brewing capacity. It doesn't matter how much beer you can brew if you can't fit people in your bar. It also doesn't matter how many people you can fit if you can't brew enough beer.
Start by considering how many seats you expect to have, aka the number of serviceable customers you can have max. Then consider throughout the day how many seats might be filled. Consider that Friday and Sat nights you might fill the place up, but monday for lunch you might only have x amount of seats per hour.
Then consider how many drinks each customer might have. In a brewpub generally people will buy several drinks because it's more adventurous than a regular bar. People who don't even drink beer regularly will ask for suggestions as to what unique beers you have and should likely order. Imagine each person might have .75-1.5 beers during off peak hours, and 2-3.5 during peak hours. Those numbers aren't founded on any sort of real life science, but it demonstrates the concept of drinks per seat which is important.
10bbl is a large amount of beer, so you'd need a pretty big sized brewpub to cycle through that much beer.
Take the average seats per day and average beers per seat, then do the math. Convert total pints to bbl and you'll begin to see how realistic your estimates are. Hope this helps!