What: Casual restaurant and brewhouse operator BJ's Restaurants (NASDAQ:BJRI) stock was up 12% at 1:30 p.m. Friday, after the company reported better-than-expected results in its third-quarter earnings report, released after-hours on Thursday. 

So what: BJ's reported that comps -- sales at restaurants open at least one year  -- were up 2.3% in the quarter, marking the fifth straight quarter of comps growth. Sales were up 11%, driven up by both new restaurant openings that increased operating weeks -- a measure of growth in locations -- about 10%, and the comps improvement. 

The restaurant operator significantly improved profits in the quarter, with net income up 90%, and earnings per share up more than double due to aggressive share buybacks over the past year.

The biggest driver of profit growth were a significant improvement in restaurant-level operating margins, which jumped 210 basis points to 19.7%, as the company's "Project Q" initiative continues to drive down costs and improve restaurant operations. 

Now what: BJ's continues to roll out a steady, if less-than-aggressive, expansion plan. The company opened six new restaurants in the quarter and is on track to have all 16 of its planned new restaurants for 2015 open by the end of November. Management reiterated its plan to open 18-19 in 2016, slightly above a 10% rate, based on the current base of 169 locations. 

And while 2.3% comps growth isn't exactly stellar -- after all, Chipotle Mexican Grill fell recently after reporting 2.6% comps growth -- the casual restaurant industry is more challenging today than it has ever been. So any growth at all is a bright spot, and the company's execution on its cost-cutting and profit-increasing strategy is getting a lot of positive attention. 

In summary, it's a reminder how perception can affect stock prices, and that performance is a very relative thing.