I believe when he went over that part in the video he was commenting to what cities sometimes do when a subway is built under a street, they rip out the tram lines at street level as a default.

I believe the comment was that if a subway is under a street it would serve less stops (greater distances between stops), where a tram at street level would serve the same stops as the subways but with two or more stops in between subway stations.

Toronto as a example has a subway with a bus line at street level. Though it only operates the bus line if the subway line is shutdown. With the two operating at the same time it would decrease some of the crowding at rush hour and allow the bus to serve the intersections between subway stops.

It seems redundant but its similar to needing to jump in a taxi after leaving a subway station to get to a stop in between stations.

Feel like it might have been talked about on his podcast "The Urbanist Agenda". He's done a couple episodes about Toronto with RMTransit.

Believe he talked about that in a bit more detail in another video about trams. I think that video was titled “Trams are the G.O.A.T” or something to that effect.

But essentially, and iirc, trams and subways serve subtly different purposes. Sure, at the end of the day, they move people between points, but the difference lies in what you can get between those points. Running trams at ground level close to shops means that they facilitate local foot traffic, and makes it easy for people to just get off and go get what they want to easily, sometimes at the moment they see what’s on their way. They can do that without the need to get up and down via stairs / escalators / lifts. Sure, you could check out a map to know where you wanna go, but where’s the serendipity in that?

Subways are great for faster point-to-point travel, especially if you don’t need to visit any of the areas between those points. Trams are generally slower than subways cause, at the end of the day, even if you give it priority on the surface, you are still close to humans on foot traffic, and there are points where you’ll have to slow down to not make people feel unsafe, even if their path is predictable.