Well, both kingdoms used to be Hindu states back then. But since Islam became an irresistible force in the 6th century spreading like a wildfire (Europe knows about this!), then it also reached South-East Asia via Arab merchants & traders.

Now I don't exactly know if the Arab merchants went by land or by sea but most likely, it's by sea 'coz if you look at any map, the countries buffering Malaysia (Thailand & Burma) didn't become Islamic since they're still Buddhist up to now.

Hence, it's most likely that the Arabs went via sea to reach this region.