Hii and welcome to TBT, Astro!! I hope you enjoy it here!
Your avatar is so cute!
I've sadly never played the OG Animal Crossing, but New Leaf is my favourite AC game as well! Kid Cat is also one of my favourite villagers! He's such a cutie patootie.
Which AC game(s) are you playing currently?
Also, like Yoshi155 said, you don't necessarily have to ping someone in order for them to see your reply! However, I'm not sure if automatically watching content you interact with is the default option, but not everyone will have that enabled (I don't lol). If you want someone to see your reply, you can also quote their post! To do that, look at the bottom of someone's post, and on the right side, you should see "+Quote" and "Reply". "+Quote" will let you reply to multiple posts at once, and "Reply" will let you reply to an individual post!