After forwarding this video to my German flight instructor friend, I received this reply:

Yes, he landed at the airport which had a runway light system.
He says that he planed to start the engine twice for climbing but
his wife as copilot was against it because at the second time it would have been too dark to see if the prop is in the right position to retract the engine! ;-) Quite clever! ;-)

Next day the engine didn't start. The crank (starter) was defect. They changed it.
Then he took off. A few minutes later the water cooled engine became too hot he landed again.
The water hose was broken. He said when this would have happend the day before at night it would have been his end.

He speaks VERY critical about this flight and his decisons!!

He was speaking at the FAI not to extend world record flights into the night!

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Of course in the USA, you cannot fly a glider without an approved lighting system after sunset, or before sunrise for that matter, by FAA regulation.