Most math students rejected His message.

Jesus says that for every number in an empty set it is true that 1=2?

That’s formally correct, any property can be attributed to elements of an empty set - for example, every unicorn currently living in my house is afraid of tea.

This is counterintuitive because for this to be true you’d expect me to have to prove the existence of my unicorns and then their phobias, but formally speaking I just need for counter-examples to be impossible.

Logically speaking the negation of “all my unicorns are afraid of tea” is “at least one unicorn is not afraid of tea”, which is not possible since I have no unicorns, therefore my sentence is formally correct. Even though people wouldn’t accept this because it is counterintuitive.

Did I get the joke?

There's nothing wrong here, usually there is a rule after the colon. So 1=2 is the rule here