I do totally get this but I don't want to spend any time around him so end up being borderline rude (like turning away when he approaches)
DH can call you whatever he likes, but its you walking the dog, & you having to deal with Intrusive Man.
Can I suggest you drop the borderline rude, & just come out with it?
"I asked you not to feed my dog, you ignored me, please go away".
Otherwise, he will carry on, you will seethe & deflect, & your dog will end up not only being fed suspect stuff but gravitating toward Intrustive Man for more goodies.
Used to have this in local woods with my old retriever.
"Please don't treat him/can I ask you not to give him treats/would you please not do that/excuse me I have asked you not do do this"
were met with "oh it doesn't matter" "aw it's just a little treat" "oh but he likes it".
My dog was young as the time & still sharpening up his recall training, Obviously that went to shreds whenever Treat Twat hoved into view. Hos own dogs had zero recall because he was the type of ineffective Twat who stands hollering his dogs names repeatedly, ie teaching them that recall is optional.
Eventually I bit the bullet & told him that it was my dog, my decision, that he was to stop fucking baiting my dog against my express wishes or he would see me get really angry.
Not suggesting you go in that hard OP, but I had the measure of my Twat, & just wanted to fuck him off.
But don't be That Woman who is told by random strangers & her own husband that she must submit to male whims bacause they're harmless, & it's your job to appease them, & who are you to decide what's good for Ddog?