I am the designer in the video. I should say that I also used to work for Adobe. And that is not to say that I don't design in PS because I think it is crap. Quite the opposite, the PS team is an awe-inspiring team of PHD-level engineers. I would say that it is a huge tool that is still focused mainly on imaging and is decades old. They have to respond to a very large and diverse user base. I personally, don't like using big monolithic tools, like most web-oriented people I like the light-weight editors and focused tools.

I was a Fireworks user, but since Adobe decided to phase out support, I looked at what my workflow would be like. This transition came at the same time that I was moving away from detailed specs to a more lean design process, leaving the details to when I switch to code. Sketch, makes it very fast for me to create mocks and for the team to switch to code. Everything I design translates very well to web standards. I know that since Generator, Photoshop has a much better export flow to CSS but that is still not how I work.

Overall, my switch to Sketch has been very positive and I would recommend it to anyone that is doing any type of interactive design. Granted, Sketch is still pretty new and is missing a few things. Symbols or Smart Objects being the biggest thing for me.

Right now my workflow is: Omnigraffle for userflows, Sketch for wireframes and sketches, PS and AI for asset creation, Reflow for when I need to try some responsive layout, Edge Animate for motion prototypes, and I'll code with Brackets.