No offence I'll just be direct here: Please be more sensible.
Who are you and why should the steward trust you? Please consider the general safety of the public.
Your case reminds me of this guy at a US airport. He was carrying this super huge thingy. I can't remember what it was, some kinda musical instrument or whatever. He didn't want to check it in. And yet, if you looked at it, you'd know it was also ridiculous to hand carry it because of its super huge size. Yet he insisted, quarreled and even made life very difficult for a female airport staff. Her other staff got to step in to help out. Finally, the colleague told the passenger: "Look, she's only DOING HER JOB!"
Yes, no photography is allowed on SQ flights. I'm surprised you (and some others here) didn't know this since you said you are a "loyal flyer of SQ". This No Photographer rule was enforced a few years ago as far as my own experience tells me. Maybe it was enforced even earlier.
I've looked at your pics. What were you trying to achieve? There's no meaning to it, either artistically or for the sake of photography. It looks more like voyeurism except that the stewardess was dressed up. Come on, stop giving the craps lament Oh what a pity, I wish to improve my skills in photography. There are many other ways to do that.
Sure, you can justify all you want that you are harmless blah blah.... But who are you? you're a nobody to SIA. If it's so easy, everyone can say I'm harmless and lurking around could be a real terrorist.
Why no photography on board a plane? That's a no brainer. This rule is being enforced in many places also eg shopping centers etc. For those who have little travel experience, or have traveled but too lazy to think much, here are some:
1. Terrorism. Photography is one means terrorists use to plan their stuffs. Nuff said.
2. Using the photos for commercial purposes.
3. Invasion of privacy/creating distractions among fellow passengers .
I can list more but please use a bit of the grey matter to help you get the answers.
I'm not sure why the caucasian got away with his flash photography. Did the steward see it? Perhaps not. If so, I'm sure he would have told him to stop taking pics also.
Sometimes, it's hard. It's not always so clear cut when photography is allowed. It's nothing to do with race or skin color.
So please don't be a simpleton and say "But I'm harmless and I want to learn my photography."