My sensor run out of battery but Cayenne still receive data!?!

Hello.

I connected my LoRa sensor, Catena 4550, to myDevice and I started some test using TTN.
My sensor run out of battery 5 days ago but myDevice still says: “Last data packet sent: March 21, 2018 9:17:06 AM” (Message on the bottom left side near Search Devices)

What does it mean? The sensor is OFF.

Thanks.

-M.