Matte issue

Hi,

I'm currently following a tutorial from video copilot here but I can't help but notice something is amiss, while following all the steps in it.

At 12:21, it can be seen that the cars in the background doesn't appear to be aligned with the original footage, because of the frozen frame matte. I'm pretty sure there's a way around this but am unsure how (tried freezing frame at later/earlier frames but didn't work).

Could someone advise me on this? Thanks and cheers!