Why is cyclopropane more acidic than propane
Indeed, according to the Evans pKa table the cyclopropane $\ce{C-H}$ bond (pKa ~ 46) is more acidic than the $\ce{C-H}$ bond on the central carbon in propane (pKa ~ 51). 

We know that, in general, the acidity of $\ce{C-H}$ bonds follows the order $\mathrm{sp &gt; sp^2 &gt; sp^3}$.  This is because the more s character in an orbital, the more stable (lower energy) electrons are in the orbital.

The $\ce{C-H}$ bonds around the central carbon in propane are close to being $\mathrm{sp^3}$ hybridized, whereas the $\ce{C-H}$ bonds in cyclopropane are roughly $\mathrm{sp^{2.46}}$ (see this earlier answer to see how the hybridization in cyclopropane was determined). 

Now, when we compare the hybridization of the $\ce{C-H}$ bonds in cyclopropane and propane we see that there is more s character in the cyclopropane $\ce{C-H}$ bonds, this explains the increased acidity.