Yes, I am of Indian origin, so I definitely look like an Indian. However, I have all the good bits of British inside me and you can only see that when I talk or with my behaviour.
I can see the logic behind what the mamasan and the expat told you, and unfortunately I have to agree, as I understand how Indian guys think.. when they actually go to places like Bangkok or Pattaya.
Keeping me aside, most of the Indian guys on their own will behave nicely and treat the working girls fairly. The fact that they went on a holiday to a different country means they are probably earning well and can spend well to have a good time. They don't need to show off anything to anyone by being stupid. This is where the good ends.
If they go to these places as a group, that's where the bad starts. They are probably trying to save money by sharing the accommodation and the working girls. This is what happens in India, as good looking escorts are expensive, they tend to share, I was told. They repeat the same concept anywhere they go. In Indian society, a working girl is seen as basically a bad girl with no ethics (same not applied to the punters though).. and if it's Thailand, they will think even worse about a working girl. Which is why they don't show any respect and can seek an unfair deal. As a group, the bad behaviour comes out after a drink or two and everyone will try to prove themselves or show off.
I have seen a group of Indian guys having one beer each and sat in front of the dancing girls for several hours. No girls approached them. I was sitting behind them with the young girl I was talking about, and several other girls were in conversation with me and laughing with me etc. This group of guys thought I owned the bar, as all these girls were nice to me and talking to me. One guy actually called me and asked me to get tissues as his drink was dropped on the floor.. I went and told him to f*ck off. He said sorry and explained that he thought I owned the bar. He couldn't believe an Indian guy can just sit on his own and all these girls are all over him.
Luckily, as I went on my own and I behave nicely and I basically told the girls that I am from London straight after a hello, meant that I didn't experience any hurdles. A couple of girls have actually asked me whether I came from London before I said it. So, I thought they can spot the difference somehow and work out how they behave with someone like me. The bars I went to, welcomed me with a smile and I did spend decent money on drinks.
After my trip, I am very confident that I won't face any issues in Thailand.