Not sure what you mean by spin- if you are moving beam around rapidly then you will only see a very short flash... this is NOT the same as pulsing it in the way they are talking about.

If - for instance- you have a 1 Watt average power laser, but you are pulsing it on for 1ns every second, then in that 1ns the power is 1GigaWatt. The energy is still 1Joule every second, its just all concentrated in that 1 nanosecond. It is in this way a laser could be made to be brighter than a star... if you are taking a spectra of the star and integrating over an entire second, you probably dont notice anything, but if you only consider that 1ns, then you see a signal that really stands out.

If you have a laser that is always on and you are scanning it across the sky then an observer at another star may again just see a 1ns blip of light, but now its at a very low intensity and likely is not noticeable even if you window on that nanosecond...