Is this powdery mildew or from humidifier??

Usually it forms circular colonies then expands, so there's hope, but also does look like it in general. keep one of the leaves, maybe outside and take a picture now and tomorrow, if the white stuff 'grew' in any way, you know it's mold. A scope might help too... a good close look should see the 'hyphea' - thread like structures coating things. use a google image search for a comparison - probably see a nightmare example in image search, so expect something less severe looking. the residue certain humidifiers cause is possible... if you use the type with a wick and forced air through it, that type doesn't deposit the white residue. The ones that spew out a visible vapor, do.