You can evacuate a contested tt, but not use such a move to attack. The tt you move to must contain one of your own units (allies do not count).
It says that in mobilize units, if you have a tt with other land units but no infantry, you must demote one unit to an infantry to fulfill the “minimum 1 inf” criteria.
It is sensible to enforce this after movement as well if you spot the enemy has made such an error.