General

I got a funny comment about my weight gain yesterday, delivered with a wink and a grin:
'You're getting fat!'

The person who said this is a native English speaker. What I'm wondering is whether there’s an implication that she thinks I’m going to get even fatter with this wording? Is there a difference between this and saying:
'You gained weight/fat'?

Are there any English speakers who can help me out?"

Question: do you know this person? Because if not, I'd ignore the interaction. Just a random weirdo.

But no. There is no difference between saying "You gained weight" and "You're getting fat." No one says "You gained fat."

Thank you for your response! I should have clarified that the person who made the comment is actually a friend I haven’t seen in a while, and our dynamic is usually pretty direct and playful. The tone was lighthearted, and I suspect it wasn’t entirely random—maybe they wanted me to think about whether I'm on a trajectory toward embracing a fluffier future. 😅

I understand that 'You’re getting fat!' and 'You gained weight!' might not carry much difference in meaning, but I was curious if the phrasing hinted at them imagining me growing even fatter. Either way, it’s been an amusing thought spiral to unpack, and I appreciate your insight!

I think that some people use laughter as a way to manage awkward feelings - like embarrassment, shame, odd amusement, arousal, and other harder-to-define feelings.

If this person is playful with you, their observation of "You're getting fat!" with a wink and a smile could be taken a bunch of ways.
Most likely it's a friendly-intentioned observation that included some awkward emotion on their part.

The word "getting" is a state of becoming, so it means that she has noticed that you have recently put on some added weight but that you haven't yet hit a point of where your identity is as a fat person.

I wouldn't put too much thought or concern into it - you should respond with, "Yeah. Do you like it?"

I think you are reading too much into what was said.
Most people really don't think much about if you get fatter in the future.
People with a fat fetish would think that way but most don't have a fat fetish.
If someone says wow you have gained a lot of weight I just say thanks for noticing and the subject ends and we discuss other things.