I don't see anything anywhere that says there's a difference for port of entry. From TIMATIC:

Visa Exemptions:

Nationals of USA with a normal passport for a maximum stay of 30 days.They must have:- a passport valid for a minimum of 6 months from the arrival date;- a return/onward ticket;- a hotel reservation confirmation.

Under this visa section, it mentions you can get a visa on arrival at the various international airports, but since I'm valid for a visa exemption, those don't apply (unless someone else can point me to something saying otherwise). The visa exemption isn't valid for those staying with Mozambican residents, so I'm assuming that's why that section is listed.