Altoria and Alberon had events transpire about which Reiger naturally had no knowledge.
Even if he knew, Reiger wouldn't be surprised.
It was perfectly normal for Alberon to doubt his own origins.
On the contrary, it was abnormal, like Altoria, who knew her origins were dubious yet never doubted herself and somehow gradually came to trust and even depend on herself.
After all, he was neither a native of Fairy Country Britannia nor from the Pan-Human History.
The stories taking place in this world are a collection of various tales involving massive conflicts between Pan-Human History and the eliminated anomalous zones; Reiger belonged to neither side but was an entirely unknown third party. It was easily conceivable that many who knew his situation would doubt him.
At the least, Reiger was sure, not just Alberon, even Beryl, who already realized that he was not the expected Chosen One but a human, was doubting his origins and making some arrangements.
