Yeah . It does look like poop . . . I just seen peoples ts have them , then they cant eat , and they die .I have seen this on ALL of our Avicularia at some point. I freaked when it was first noticed,but it did no harm.Odds are it was poop/tarantula vomit( if they are capable of regurgitation, I haven't the slightest clue))If the white stuff is not moving/squirming,I would say your T is fine.