There's a difference between AC and DC charging. All current Tesla's accept 240 volt AC and there's no reason to expect that the semi won't either but with the such a giant battery pack 240V will simply not be fast enough. The 1000 volt is for DC fast charging. Tesla's current models use 350-375 volt battery packs. 1000 volt will just allow them to charge faster for DC fast charging, and more efficiently.
To add to this, for AC, there is a conversion stage (ie inverter) that needs to convert it to DC to charge the batteries. This unit, at the currents that the Semi requires to be charged in a reasonable amount of time will be wasting too much energy in conversion losses.
Due to its inpracticality, AC charging is unlikely to be an option, but maybe they include it for those exceptional circumstances.
