Hi HUmfrey,
Strangely enough I was reading some references to the Humfreys in another book I have and it said Charles was the only son of Mayor Charles and that he, the son, went to Downing! Sadly the other 4 sons had died very young. 3 daughters appear to have survived. For some reason the writer of the diary I was reading nicknamed the son Charles 'Enthusiasm', this was around 1833/36 so he was in Cambridge then.
I will write more this evening, I started to draft out the case to prove the relationship - I feel certain now that you are on the right track!!
Selina