Was I in the wrong here?

I babysit a little boy who is in kindergarten. The other day I was reading books to him and he wanted to "read" Polar Bear Polar Bear What Do You Hear to me (he was just going off the pictures and memory). There's a flamingo in the book and every time he said flamingo, he pronounced it as fluh-bang-oh. I corrected him and told him how it's pronounced.

I get here today and the mom is mad that I corrected him. Saying I had no right to correct her child. Obviously I get he is her kid and she makes the rules, so now that I've been told, I guess I won't correct him anymore. But was I wrong to have corrected him in the first place?

I wasn't mean about correcting him in any way. Just letting him know how it's supposed to be pronounced and he wasn't upset or anything. He understood I was helping him.

If he was younger, I may have just let it slide and let him say it his own cute way, but he's in school now and learning to read. He should know when he pronounces something incorrectly and how it should be pronounced.

I don't have kids yet, so maybe I just don't know, but I feel like I would want people to help my kid talk correctly.

I'm 28 years old and have worked with kids most of my life and the way she talked to me just made me feel so stupid and small.