This sounds very misleading, Riemann was no lesser genius than Einstein, what in the end became this mentioned lecture was certainly not done in a "lazy afternoon" and in fact the paper of his based on this lecture started a major revolution in geometry and is considered to be one of the most important papers ever in this branch of mathematics. What more would you expect? Riemann wasn't a physicist...
Source:
http://en.wikipedia.org/wiki/Bernhard_Riemann#Euclidean_geom...
In 1853 Gauss asked his student Riemann to prepare a Habilitationsschrift on the foundations of geometry. Over many months, Riemann developed his theory of higher dimensions and delivered his lecture at Göttingen in 1854 entitled Über die Hypothesen welche der Geometrie zu Grunde liegen ("On the hypotheses which underlie geometry"). When it was finally published in 1868, two years after his death, the mathematical public received it with enthusiasm and it is now recognized as one of the most important works in geometry.
By the way, read this paper of his. It has very little formalism, doesn't presume a lot of background knowledge and contains many brilliant insights.
http://www.cs.jhu.edu/~misha/ReadingSeminar/Papers/Riemann54...