Too close for comfort. I don't know what the braking distance is but I doubt 60-70 tons of steel at up to 70 km/h are that easily stopped. If that truck had to suddenly do an emergency brake, then the tank would probably just roll over & flatten it, with everyone in and on it.
At 70km/h, 20.6 metres. For ordinary cars it's ~50m.
In a nutshell, a tracked vehicle has quite a bit more contact area with the ground, it's also kind of hard to lift the rear wheels up so you can apply a lot of break force before you start to skid etc. And Leos have the hardware to actually do that, there's a retarder in the drive train and additional disc brakes.