Accept this input with the caveat that I am still a novice, but molds will be a pronounced color like grey, brown, greenish and often form hairs. Brett is white, cream, even towards greyish but powdery and chaulky looking. The images look like a pellicle after the carboy has moved a bit. When I even nudge my carboys a few inches they break into what your photos look like.
I wouldn't worry about it. Something I haven't gotten to yet is to purge the headspace of secondaries. Molds are mainly aerobic and will hinder their development so the brett can do its thing.