iMessage iPad WiFi SMS from non Apple phone

Recently, it seems that SMS messages to my iPhone, from non-Apple devices (green text bubble) have been showing up on my iPad. The SMS messages are not synching, in that they haven’t updated, in several days. i was surprised to see messages with green text bubbles, on iMessage, on my iPad. Is this new, or have I not been paying attention, for the past 10 years? Why, if they appear, do they not update? Most recent synched (Green bubble) SMS, on the iPad was 4 days ago. Have newer messages, in same thread, on my iPhone. Any info appreciated.