That looks like Cecal poop. Chickens have 2 types of poop - Cecal and "normal". Normal poop is firmish/formed poop with a white cap (urates). Cecal poop is a loose poop that is stinky, pudding like and sticky-it also varies greatly in color. A chicken poops a Cecal poop about 1 out of every 8-10 normal poops.
Looking at chicken poop is very good! Poop can sometimes tell you a lot, so keep that up. Behavior is also an indicator of something going wrong - if your chicks are all active, eating, drinking - then usually all is well. If you notice any lethargy accompanied with huddling/fluffing up, distress peeping or not eating/drinking, then there is cause for concern