That means that your piggy didn't eat enough and had a bit of a tummy upset from the GI stasis when it hit; it is perfectly normal to see funny poos coming out at first once the gut gets going again. What you are seeing right now is the debris from the damaged zone when the internal conveyor belt hung up.
You should see the poos gradually normalising and getting thicker over the next day as the syringe feed is more and more reflected in the output.
That is the reason why weighing on the kitchen scales is so important - that tells you what is going on RIGHT NOW.
The poo output can only ever tell you what has happened a day or two before but it is very much running behind events. In your case, it is only proving that your vet has got it right with their diagnosis and that the stasis 'gap' on the conveyor belt is now over