Why doesn't propynal give cannizzaro reaction?
It is known that terminal alkynes reacts$1$ with $\ce{NaNH2}$ and produces salt, much like an acid-base reaction, hence it is a fast reaction.
Furthermore, the aldehyde group is an EWG, which makes it easy to lose a proton, hence drives the reaction!
Whereas, cannizzaro reaction happens through multiple reversible steps as seen in the following image,

Therefore, acid-base reaction in this case has much higher probability than Cannizzaro reaction.

References
$1$: http://www.chem.ucalgary.ca/courses/350/Carey5th/Ch09/ch9-2.html