Yep, people can he negative about someone else's weight loss. I worked with someone who lost a significant amount of weight and got told she looked gaunt. By someone else at work who had a reputation for being a cow. She didn't she looked great.
I asked if she'd had the opinion of someone she listens to. Yes she said smiling. Enough said IMO.
I assume people envy someone's deliberate weight loss success just because they've had some success, about anything.
(I think people who have successfully given up smoking and become a non-smoker can get torn down by their fellow smokers too.)
I once lost a lot of weight and got called a bitch for no good reason.
People get envious of other people's lives/car/children/financial position in life/partner etc etc etc. Successful deliberate weight loss is just something else for people get envious of, it seems to me. Like I said, envious of your success because you've had some.
Who gave you permission to lose weight ? It wasn't them, was it ? Especially if they take the view that you've lost weight to attract or keep a partner. Or worse still seem to think that you've lost weight to attract their partner - who you've never seen & probably wouldn't want them if you did.
If you've been the 'fat friend', the bench mark of, 'I'll never be as fat as her/him' then it upsets their particular apple cart that you've gone and lost weight. Well that's not on as far as they are concerned. Even if you've been nice to them for various reasons over the years.
The implication could be, 'why don't you lose weight like she did ?' Or She's lost weight why don't / can't you ?'
So you may have created work for them unwittingly. Some people are very precious about 'the slim club' (no such thing exists, I just made that up) and don't care for new members to come from fat and happy. The overweight are there to be sneered at as far as some are concerned. Not lose weight and start getting attention.
Just you keep on doing what you were doing. THIS GIRL CAN DID.