Why is the nutrition information for these two items so different? (In the UK)

I have a packet of custard, which has the following ingredients: Maize starch, salt, Flavouring and Colour.  The salt content on the nutrition information is 0.17% so I assume that the custard is almost entirely Maize Starch.
Wikipedia tells me that Maize Starch is the same as (in the UK) Cornflour. I have some of that in the cuboard and its nutritional information looks like this:

My question is: why is the nutritional information so different? Where did the Sugars come from? Why is there more protein? What's going on?
You are comparing (100 g of custard made with some of this powder and some milk) to (100g of this powder) -- ignoring the salt, anyway.
The magic words are

As prepared with semi-skimmed milk

That's where the sugars and proteins come from, among other things.