Today morning, I got a prompt asking me if I wanted to enable chat features on messages app. I did that and saw the info on the SMS sent yesterday. Dug, to know more, and here's the summary from the Google FAQ on chat features :
You need the messages app as default SMS app.
Chat features are support is region/country/carrier specific.
When using chat features, your messages are sent using the Rich Communication Services (RCS) protocol over Wi-Fi and mobile data.
- Show you when someone is typing
- Offer read receipts (show when someone has read or received your message, as well as showing your contact when you read their message)
- Send messages over mobile data and Wi-Fi
- Lets you share files and high-resolution photos
Sending over Wi-Fi doesn't cost, over mobile data will be as per mobile data plan.
To answer the question, recipient doesn't have this feature enabled on their app and therefore SMS was not sent over Wi-Fi or mobile data and sent as normal SMS. It is only highlighting this aspect. Similarly, if you were to send MMS content in the same situation (feature not enabled, data not used), it would show as
If chat feature is enabled and sent by data, it would show mobile or Wi-Fi as the case may be.