I agree, that looks like normal brown diatom alage which happens at the beginning of your cycle. If that's what it is, it will disappear within a few weeks.
Cyano is slimy, and is often red or green. You'll notice it begin to trap bubbles, at least it did in my aquarium. If you disturb diatoms, often they will seem to vaporize into the water. Cyano will come off in slimy clumps.
Paul