I have run through set of Shinko 705 on my Tenere 660 on a RTW trip. Amongst others I did The Gibb River road (an 800 km outback road in northwestern Australia, which more than 650 kms is gravel/sand/mud including some challenging rivercrossings etc) And the Shinkos also were on the bike through the last half of Indonesia on the same RTW trip - and the tyres did perfectly well for what they are, a 80/20 on/offroad tyre. In the roughest part of the Gibb River road I wished I had something more knobby-ish but except from that they were totally ok, I had no issues in the wet with them.
I think paved roads in Thailand for some reason or another get very slippery when wet, much more than other places in the world. Just look at the amount of cars in the ditches during or right after a rainshower in Thailand. Thaidrivers are maybe not all that great but they cannot by all means be that bad either...
Maybe the mixture of stuff thats used in asphalt in Thailand are a bit different compared to asphalt used other countries so that the roads get more slippery when wet? Maybe the heat does something to the asphalt when it get wet so it gets slippery? I dont know, but thai roads get very slippery when wet. Personally I think thats the problem your mates had when riding the Cb500Xs with Shinko 705 tyres, not the tires themself.
Then again - something I have learned about tires and choice of tyres is that it is very personally. Just like what music people like or what food people like. When it comes to tyres its exactly the same.