Certainly it should be an indication to pay a little closer attention, but probably just like outlier data, it's not an issue.

I think you've already been involved in some posts that mention it, but just to be sure, many suggest not to feed them "red wrigglers". They say that that type of earthworm excretes a very bad tasting slime that might cause your FBT's to shun all types of earthworms.