While it is true that very few could know who apart from Andrew was in the carriage, a city as large and important as the capital of the Cannaris empire has very powerful people hidden.
Like most major cities, several demigods live nearby and they could notice Elder Hacta's aura from the moment she arrived in the city, so they were alert.
The demigods were not controlled, nor under the rule of kings and emperors, but that does not mean that they do not have shared interests with the countries.
It is for this reason that many demigods live near this city and are willing to intervene if something extraordinary happens. Since the emperor had had a full week to plan this meeting, he contacted some nearby demigods for support.
