Extra toes are found in many breeds actually, not just silkies. Dorkings, Favorelles, Hodens, Sultans... I think Silkies and Salmon Favorelles are probably the most common toe-adders in backyard chickens- so it likely has those breeds mixed in there.
If the chick is still eating and pooping and alert (when not sleeping in your palm) then you're probably in a pretty good place at this point. Most that die at this age do so relatively quickly. Their health declines fast and they get that lethargic/sleepy look and pass thereafter. So hopefully you are out of the scary part of the woods... but there are still trees around you for sure.