As TJPhilly remarked:

[SIC] Have you considered the possibility that he died outside of Pennsylvania? New Jersey and Delaware could be possibilities, especially if he had family in either state.

In 1933, it may have sufficed just to have a death certificate from another state to bury an individual in Philadelphia. [Earlier burials up to 1915 appeared to want a certificate from the state of the individual's demise along with a Death Return from Philadelphia.]

Is it possible to locate the name of the undertaker from the (New) Cathedral Cemetery records? Did you happen to see the actual record book or just the print-out of the burials? I was chasing a relative that according to the print-out provided by the cemetery, died in 1998 in lieu of 1888. If this person was a close member of a Philadelphia family, then what parish did they live in? Maybe the church has a record. Knowing the neighborhood may clue you into who the undertaker might be.

Could he have been a member of the military? [veterans burials]

It's just possible that it 'fell through the cracks' since his name could be BRYAN/O'BRIEN.

Good luck,

Frank