This may be great for some people, but simply isn't true for others. I've found no difference on focus from working out, even heavily. Not from getting up and walking a mile and going back to my task.
On the other hand I find it relaxing to workout after work. My mind becomes more or less empty afterwards. When I then do things that require more complex thinking the effect wears off pretty quickly though.
It also wears me the fuck out - so I go to bed early, sleep really well, and wake up the next day feeling recharged.