It's said, that two classic cars were destroyed, but there's only one to see:
https://www1.wdr.de/nachrichten/rheinland/brand-siegburg-reportage-100.html

Some US-car from the early 50ies.

About the incident: a fire directly nearby the ICE railway line Cologne-Frankfurt Airport, probably caused by sparks. Or broken glass. Or a cigarette.

In Germany we have unusual drought and heat up to 40 degrees since some weeks.