As the title says, Brock showed the most concern for Charmander throughout the episode which Ash even pointed out but Ash ended up catching it. I had already seen episodes with Ash's Charizard before I saw this particular episode so I already knew he would catch it but if I had watched the episode blind I would've thought Brock would catch it. If I'm not mistaken Brock said Ash deserved Charmander because Ash made sure the flame on his tail didn't go out. Just an observation I wanted to bring on here. It's probably for the best anyway. Charizard ended up being one of Ash's strongest Pokemon. I don't think he would've reached his full potential under Brock as he didn't battle much.
Side note, someone should really look up Brock's win to loss ratio excluding Team Rocket battles. I have a feeling it's not very good.