WhatsApp sends messages by itself?

I recently wrote with a friend and then switched to another app on my cell phone while WhatsApp desktop was still open on my laptop. When I checked WhatsApp again a few minutes later (on my laptop), I had sent the message "oiso at least for wine" (translated from Austrian colloquial language: at least for wine). The message was completely out of context, I hadn't written it and it was in both my and her chat. I was home alone and no one else could have written this message.

What has happened there? Have i been hacked? Was that a WhatsApp mistake?

Settings → WhatsApp Web. Look in here.

That was open somewhere, someone wrote something in there. Otherwise not possible.

Virus or check how many apps you have allowed to access your media and deactivate them

So I'm pretty sure that Whatsapp doesn't accidentally send messages in correct Austrian slang. Do you think there's an AI sitting there practicing dialect?

If it wasn't you either, then the only thing left is someone else who has access to your Acc. Would have.

For everyone, the famous Ösi Trojan. Captures strangers Whatsapp and randomly sends Austrian slang messages to all contacts.

"A pack of Hausdetschn sand the same chunk."

That has already cost marriages.