There are very few chunks that are very large, religious monopolies dont exist on the plural internet. The largest single one is atheist, unsurprising given that twitter is dominated by wealthy Europeans and Americans, and that the internet in general is great at getting atheists to gang up and crash polls of this kind. Another thing to notice is how far from negligible the small religions are, pagans account for whole 3%, wiccans another 2%. The raw data gives you an idea of how important this effect is, even the smallest group represented: Confucianists have 26 votes to their name.
So the raw data give us, dont ignore the little guys, there are atheists on the internet.
If we categorise religions however, we get another couple of ideas, again, not very suprising. The largest group is the broadly non-religious including agnostics, followed by the Christians, then the other Abrahamic religions, (note that this is 12% Islam and 2% Judaism), then the others, still an impressive 14%.
What can we work out from this? That the representation of Islam is a lot lower than you would expect from world totals, likewise the other major world religions besides Christianity. This is at least partially explained by this poll being run in English, ask the same question in Arabic or Hindi and I'll bet you'd get a different result. The rest might be explained by the penetration of the internet in various countries and social groups. Obviously there are far fewer Buddhists and Confucians than worldwide figures would make you expect because of the Chinese internet, likewise African folk religions.
One thing that might be interesting to note is how massively over-represented is the category "Other Christian". Roughly speaking the other categories are in the right proportions to eachother, but other is at least an order of magnitude too large. Is this tendency for people of all branches of Christianity to call themselves Christian even to put themselves into an "other" category something that is well known and studied? I can understand this result happening if there was a label "Christian", but the assumption of the poll is that you should select a denomination so people are actively rejecting such labels.