Interview via instant messaging?

I had an interview with a company, but the entire interview was via Teams messaging. Is this normal? The company is relatively well known and is a publicly traded company, that's why I wasn't too skeptical, but I am a little more skeptical now. After the interview, they also said they'll tell me whether they hired me or not in the next 20 mins, which was odd. So, is this a scam or is this something that happens?