The first part of it is not true (but the second part is true, in that you can access chats from Gmail as well).
I just checked, and Google Chat exists as a separate app on iOS, Android, and web (chat.google.com). Even though the web version redirects to a gmail url (mail.google.com/chat), it is still a separate web version, not embedded into gmail. The only thing it shares with gmail is its subdomain, the page itself has zero mention of gmail or any gmail-related functionality.
I used to have this app installed, then one day it started telling me I had to use the GMail app for chat instead.
I wouldn't be surprised to hear that they were rolling the out the migration to accounts incrementally, or they've reversed course. But I deleted the google chat app because it wouldn't let me use google chat.