...do y'all know why this might be and were these minted in the Netherlands?
I don't know why the coins were of different sizes. Perhaps specifically to prevent the two coinages from mixing in circulation, either in the Netherlands or in the islands.
I do know the Antillean coins were and still are minted in the Netherlands. You can see the small control-marks or privy marks on all Nethlands Antilles coins, indicating they were minted in Utrecht.
The Netherlands Antilles was officially abolished in 2010, but they have only just now announced plans to introduce a replacement currency later this year, the "Caribbean guilder", for use on the two remaining islands that still use the Antillean guilder, Curacao and St Martin. The other three former members of the Netherlands Antilles (Saba, St Eustatius and Bonaire) have already all officially switched to using US dollars.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis