Whatsapp chat history shown to another account on the same device

whatsapp.txt

1. I had my whatsapp account on iphone (***8)
2. I logged in to whatsapp on an android
3. On iphone, the whatsapp session was terminated. Web session were terminated. 
   All chat history were gone. This is fine, by design.
   (Note, I didn't turn on cloud backup feature for whatsapp.
   I didn't turn on icloud feature for whatsapp -- if any)
4. I uninstalled whatsapp on android
5. I logged in to whatsapp again on iphone (***8)
6. Whatsapp denied, told me that I had just logged in.
   I could retry later, but then the verification code (sms) never arrived.
7. Totally upset, on the iphone, I used another phone number
   to register myself and log in to whatsapp. Phone number is (***6)
8. I now can see all chat histories of my old account (***8)
9. included group chat, though new account was disconnected from the group(s)
10. I tried on web, chat history is the same on my iphone.

Basically, Whatsapp *securely* thinks my (iphone) device was not mine (6, 9)
at the same time it believes that device was mine (8).

This is just double-standard isn't it?