R.J.
The homeless man WAS stinky.
It sounds like your son's drawings WERE scribbles.
It sounds like the mom is trying to teach her daughter not to run around 'shouting the truth' / hurting other people's feelings / trying to teach empathy. AKA she's reprimanding her.
To me that sounds like a GOOD thing.
ADDED:
Do know, a LOT of kids, although definitely the minority struggle with drawing and writing. My son's one of them, although your son sounds like he probably isn't. Some kids just don't like drawing (which would be easier than seeing someone criticize something your son DOES like, but isn't very good at yet), and some kids -like my son- just can't. He can do a lot of really amazing things, but drawing isn't one of them, and writing isn't on the list of things he can do well, either. He has no problems with fine motor skills, he has a LOT of problems with 2d representation. Can't do 2d puzzles, or tangrams, either. (Although he has amazing 3d skills, and can do 3d puzzels so fast he looks like he's randomly grabbing pieces, and *bam* done). He's gotten a lot of flack over those 2d puzzles/drawings/handwriting by both sneering and well intentioned people (kids and adults) over the years. 2 things we've worked on are
1) Anyone starting out, or learning, isn't going to know as much as someone who's been doing it for months or years &
2) People are good at different things.
Why am I bringing this up? Because you can't make your friend use a different 'catch phrase' when she's disciplining her daughter/ can't control other people... but you CAN keep the spark going in your son if his confidence wavers. It may or may not. If he DOES star getting upset that the other kids are better than he is...
... you point out #1. "SuzyQ's been drawing for THREE YEARS. Wow. Can you imagine where you'll be at in THREE MORE YEARS??? You'll be a big 7yo! Wow. You'll x, y, z, a, b, c. by then!"
... and then invoke #2 "You know JohhnyB? He doesn't even LIKE to draw! But he likes (insert something your kid hates). But you hate (insert the same thing) and love drawing! We all like different things. And we're all learning."