Nelson, minesweepers were heavily used by the IJN during the Indies campaign in various roles, like convoy duties or even submarine patrol. On several occasions were the large and heavily armed IJN sweepers mistaken for DDs or CLs:
20 February 1942:
Alor island. At 0243, USS PIKE attacks what LtCdr New misidentifies as two "light cruisers". The ships, in fact, are W-7 and W-8. LtCdr New fires two torpedoes from 4,000 yards, but they miss ahead. The minesweepers move out of range before he can set up for another attack.
24 January 1942:
At about 0245, USS PARROTT fires eight torpedoes at W-15 that she mistakes for a destroyer or cruiser. USS JOHN D. FORD also fires a torpedo at W-15 again.
Anyway it's not worth discussing this without a good map of all IJN and allied ships in action in the Java Sea. Maybe something will pop up then...
Anyway I never said it WAS a minesweeper, just that it was not unthinkable.