I agree with the other answers that in general intramolecular reactions are faster than intermolecular reactions. Let's look at why this intramolecular reaction might be fast.
We can describe the Cannizzaro reaction as the delivery of a hydride from an anionic hydrate to a carbonyl group. The reaction shown certainly meets those criteria. I see this reaction as a carbocation rearrangement or a (semi-)pinacol rearrangement. In the latter class of reactions, a group undergoes a 1,2-migration to quench a carbocation and generate a carbonyl.
In the phenylglyoxyal rearrangement, if the ketone is considered as its ionic resonance structure (2), then the ketone carbon is a carbocation. We know that hydrogens can and will undergo 1,2-migration if the resulting carbocation is more stable. In this case (3->4), the resulting carbocation is very stable, because it's really a carboxylic acid (5). Furthermore, the carboxylic acid will be deprotonated rapidly under basic conditions (5->6).