Just to add context, the Chinese company only owned one set of locks. The canal has multiple sets of locks meaning China didn't control the canal and companies/countries could use the other locks to make the crossing.
hypothetically, since the US is the largest user of the Canal, should a China-loyal company managing one lock stop allowing US shipping through, the time for US-bound ships to traverse the Canal would increase by 33%. If the canal that's denying US access happens to be the largest lock, some US ships may not be able to use the remaining two locks.
Look up Panamax, New Panamax and Super Panamax size limits. One of the locks is the largest of the three, meaning the largest ships are not able to use either of the other two locks. In most cases, there are only a couple of feet clearance between the ship's sides and the walls of the canals.
https://en.wikipedia.org/wiki/PanamaxIn a nutshell, only one of the locks can handle the largest ships of today. if China controls that one, the other two would not be sufficient, even if the US controlled both.
The other issue is that the largest ships going in opposite directions through the Canal must travel though the locks in alternating fashion. It's basically like a one-lane bridge where traffic must take turns crossing. Imagine if only non-US ships are allowed to use the locks before any US-related ships are allowed to continue.