Russian lakes and marshes contain vast amounts of WWII vehicles and artillery (and, possibly, stuff left from all the way back to 1812). Something like his happens on a more or less regular basis.
As for getting the tank started after just a cleaning job... German engineering may be precise, but Russian engineering is friggin' sturdy. As an example, one of the stress tests on an AK-47 involved dumping it into a marsh, pulling it out a year after, cleaning it and firing a test clip with no jams. I am not surprised something similar happened to a tank.
I make proud for my country
As for getting the tank started after just a cleaning job... German engineering may be precise, but Russian engineering is friggin' sturdy. As an example, one of the stress tests on an AK-47 involved dumping it into a marsh, pulling it out a year after, cleaning it and firing a test clip with no jams. I am not surprised something similar happened to a tank.