Functionally the main difference between Monero and Zcash (esp. after RingCT is integrated) is that Zcash has a larger anonymity set at the level of individual transactions (all previous users) than Monero (some randomly chosen subset of previous users).
tldr, these are both serious, credible cryptographic techniques to deliver private transactions, with different advantages and disadvantages.
That insolent banned narcissist claimed the main difference is that the IP address and other markers of activity could be correlated to specific UXTO on the ring of potential payers and that this was not possible in Zcash. And he arrogantly claimed that this was some fundamental distinction. Thanks for the clarifying slogan.