Getting more and more confused here
The only thing I can say for sure is that the AD9984A asic that I am using as ADC does not alternate its field bit (e.g. it is fixed at odd or even field all the time) when receiving data from Amiga unless Amiga is explicitly set for interlaced graphic mode. Then the field bit will alternate.
This makes me believe that the output is indeed, normally, progressive from Amiga Video Connector.