When facing a loss like this, it's normal not to be able to talk about it right away, often the very first thing that is experienced is shock.

Also, it's not unusual for someone to prefer texting when they have a tendency to be shy verses instantaneous with interactions and conversation. With a text a person has time to think about their responses and they prefer having more time like that.

Give him some time and space to process the loss of his mother and all that entails with family and planning a wake and funeral etc. It's better that you don't present him with yet another loss. You can step back from that and just give him time to focus on the loss of his mother first.