Some embassies/consulates issues -as an example the in Norwegian Thai embassy- Tourist visa without any onward ticket at all and some altså with onward ticket within 90 days. The formal requirements anyway is an onward ticket within the initial days you get stamped in for in the immigration.
Onward ticket are a formal requirement for tourist entries, rarely checked in the immigration but they ask from time to time. Because it’s a formal requirement and the airlines can be fined and responsible for the passengers return if formal requirements aren’t fulfilled they normally will be more strict regarding this requirement. But the point here was requirements and e-visa.
You print out the e-visa received as a PDF file and hand it over in the immigration. Only Non Immigrant and long stay visa are excused onward ticket requirements.
He probably applied for the initial 90 days Non O at the embassy at home before he entered TH, but it still makes no sense. And they could fix it with 2000 baht…