Are you sure it was "Contemporary Philosophy"? Newton and Leibniz aren't exactly contemporary...

They should be contemporary since they were of the same era and knew each other.

I'm not sure if this is a joke or not.

They were contemporaries of each other, but they are not Contemporary philosophers as in part of the period of philosophy that is contemporary with us right now.

(I wonder how long into the future we'll have to go before the likes of Hegel and Frege aren't considered "Contemporary philosophy" anymore; or if they'll remain "Contemporary" and we'll move on to "Post-Contemporary" philosophy the way the Continentals tried to do with Modern philosophy).

I don't think Hegel and Frege qualify as, or are generally considered to be, contemporary philosophers today. "Modern" perhaps....

The two main schools of Contemporary philosophy are the Analytic and Continental schools, of which Hegel and Frege are (at least arguably) the first figures. I know there's debate about whether the Modern period has ended or not, but on those accounts where it has ended and we're now in the Contemporary period instead, Kant is usually seen as the end of the Modern period.

I guess I've also just implicitly answered my own question. The current period of philosophy will end once the Analytic-Continental divide is resolved, and this period will retroactively be called something else, while whatever is going on then will be the new "contemporary".