Paolo replied to my question via email - here's the full quote.
Pigmento is a set designed to work in both AP and AD.
The differences in using these in AD or AP are the following:
1) Automatic Tool Selection
In Affinity Photo the brush preset will automatically pick up the needed tool to obtain the wanted behaviour.
This tool is shown at the end of the sample stroke, by its icons.
In Affinity Designer this does not happen, because this feature is not yet supported, so you're free to select the tool yourself (any painting tool available) using that icon as a "hint".
2) DAUB® Pigmento - Spatula
In Affinity Photo tools from this set rely on the Paint Mixer Brush, and allow you to mix colours
In Affinity Designer this does not happen, because the feature is not yet supported, but you can always use them without the mixing feature.
The look you're seeing in my speed painting is perfectly achievable in both AP and AD.
Let me know if you need more info!