Calling a child greedy

It depends how it is said. I don't think it's a bad thing to clearly label behaviours (not the child) as a statement of fact. DCs need unambiguous and constructive guidance to be healthy/kind/functioning members of society. Greed, in any area of life, is not a good trait and DCs should be clear on that.
If the meal was an appropriate portion for the DC's age and activity level, then having more is indeed greedy. Was it said as an "absolutely not, you greedy little pig" or a "no, you've had a fair portion already and to take more would be greedy" kind of way?

It’s a mean term, intended to shame rather than teach. so shouldn’t be used, especially in front of others.

My 3 year old is “greedy” in that he is obsessed with sugary snacks and wouldn’t stop taking them until he was sick if we let him. He’s slim and a normal weight (bit on the small side if anything). We are teaching him that you can only take 2 of anything, no more, because sugar rots your teeth and also because you need to make sure you leave plenty for others. He is slowly getting the message, no shaming involved.

I think if you only provide children with real food, not processed stuff, then you would find they are very good at regulating their food intake. No, it's not helpful to call a child greedy, just don't give them access to crap.

Was the child called greedy to their face, OP? In what tone? Or was someone else referring to them as greedy?

The child's weight is irrelevant. It isn't right to call any child greedy. If another portion is judged to be unnecessary you just say "No, some more of that wouldn't be good for you. If you're still hungry you can have (whatever healthy filler you see fit)"

That isn't the point, though. The point is that it is inappropriate to call a child 'greedy'. To do so is to potentially set them up for a lifetime of food issues.

Yes, very rude, as it shames the child. An overweight child will never be helped by being called greedy.

If it’s wanting to fill up on extra crisps/snacks etc it’s very different to wanting a bit more of a proper dinner or if they’d been given a small portion. Kids can still be greedy same as adults can, teaching healthy attitudes to food in general is a better way to address this.

Yes I think it would be rude in that I can't see how it could be said with love. It sounds like an expression of disgust.

However, if there is a tendancy by the child to over indulge and/or be inconsiderate in taking more than would be available for others - it is an important part of socialisation so they have basic manners. This is for the comfort of the child themselves as well as others

I suppose it could be rude. I've referred to and heard other people refer to children as greedy and never thought anything of it, it's usually in a lighthearted way unless they are being greedy as in taking food that isn't theirs or more than their fair share.

Healthy children outside of toddlerhood (and muscles from sport) are naturally slim and slender. The judgement of "visibly a bit chubby" probably means they are in fact overweight.