If a label doesn’t say “As Prepared”, then you can assume it’s “As Packaged”. So 100g dry, in this case.
“As Prepared” refers to preparation following the package instructions. This is also why many cereal labels will also include a column with something like “Prepared with __ cups/mls skim milk”
It would be as is, unless otherwise stated.
If you add water to 100 grams of oats and then cook it, you will still have 100 grams of oats. Even if the net weight of the cooked portion has increased due to water weight.