[NoBox]

Where were you guys earlier? No matter.
I am not using BBM in a corporate server environment so my BBM is different than what you may be used to,

As for the blog. It appears to be a hatchet job based on something other than what is issued by WhatsApp.
According to WhatsApp their code is open source and available to anyone to check. The title to the page is: "WhatsApp Open Source"
Backup on the version I have backs up to a file on the device itself. As an Option I can select backup to Drive. I didn't.
There is an option on install regarding contacts. One option allows access to all contacts in the device's phone book. The other does not. If the user selects no access then each contact must be entered individually. Perfectly reasonable.
Metadata is a whole different issue. WhatsApp makes no claim about that. But, metadata is exceedingly difficult to prevent. Some folks think that accessing some kind of redirection or masking site helps. It does. But mainly for the target of the message.

As of this writing I have seen nothing that supports the assertions made by the blogger you cite.

On the other hand I found BBM to be awkward and difficult. Stickers and Channels? Come on!