Is dnd a red flag?

This guy I’ve known for a couple of months suddenly puts his phone on dnd a lot. When I call him it usually rings. But now when I call him and the phone goes straight to voicemail. But he calls me back seconds later. So I asked him what’s wrong with his phone after it happened a few times and he says he has it on do not disturb. I asked why and he says no reason. I hang up for a few minutes to do something and called him back and it’s back to ringing.

Is dnd a red flag?
Post Opinion