That would a reasonable thing, perhaps even a good sign. Lots of data for pilots comes that way these days - more easily updated than paper - and tools for (mis)calculating various things like weight limits and density...

He does mention a miscalculation. He's probably taken off enough in that plane to believe he understands its actual performance vs calculated numbers, and with a long runway he was probably thinking it ought to work and there's plenty of runway left to try a little more...

He probably doesn't get a trouble on a short runway because he'd abort quickly. That longer runway seduced him into eating into margin.