It suggests to me that that the men were raiding other peoples, and bringing home captured women as wives.
May have been some of that, probably from a different linguistic group. /stealth rimshot
Warfare or raiding parties to capture women seemed a likely possibility.
However, the nature of agriculture should also be considered. Two different crops were stated as primary in two different places. A lot of rice is grown in flooded fields. This requires an established water system and established fields. I suspect this agricultural method requires a lot more labor to create and maintain than dry land agriculture which the other crop would use. There is also the question of which type of agriculture requires more male or female labor. If rice agriculture is more costly in labor to establish and maintain, then the men would try harder to hold on to it and not move around. I have also seen photos of women working in the watery fields and planting individual clumps of rice sprouts. This is a much lighter kind of labor than managing large animals to plow packed earth. Thus it would make sense for rice growing areas to have the stable male population with imported females. Was this in fact the case?