That sounds like some grout residue left from the cleaning process. Go ahead and clean that off.
If the water doesn't bead, look to see if the water darkens the grout pretty readily or not. I find that some sealers don't make the water bead much, but still keeps the grout from darkening with the water. If the grout quickly darkens with water (like water darkens a dry concrete sidewalk), it's not sealed.