I have had a colony for years that has occasionally done this with the white stringy things. I have never had nudis and the piece has never suffered any real damage from it. I've seen them when its gotten burned from ALK, when I've accidentally dropped it, or something on it (don't judge, it happens! :wink

. If you've already dipped it and nothing came off, examined it and didn't see that you missed anything, and then continued to keep an eye on it and watched it go back to normal (as I did), I wouldn't be concerned. I'm sure that there is a lot of things that our corals do that we don't understand...
For example, My larger acro colonies looked like they were hemorrhaging for a couple of weeks and I looked for bite marks, I looked for nudies, I looked for red bugs, etc... Then I looked at it a couple of weeks later and I noticed that the parts of the acro that had looked bad had bulked up a lot. My gf panicked and thought it was going to kill it but I've always had the mentality that if its not dying quickly, I kinda let things roll