If you look closely at the video, you can see the payload free fall. In about 7 or 8seconds you can see a series of small flashes trailing the payload. I believe these may have been explosives detonating in or on the sensor packages, destroying them. They could have been triggered remotely or by an altimeter which triggered self destruct mechanisms once a certain descent velocity was attained.
Good catch.
Yesterday someone predicted the Chicoms did NOT want anyone to see the devices they sent to spy on us (or release more bioweapons or test decoys).
I joked the US could send the devices to the Wright Patterson hangar like the ship that crashed near Area 51. Veterans from the era pointed out the left rear corner where the ship was once set down (on Ancient Aliens video).
Or just a reflection off the solar panels.