In hindsight, it's pretty interesting to see how Frieren could be so sure about Fern and Stark being able to deal with the demon Lugner, since she knows well both Fern and Stark but also knows about Lugner, since they met before.
That, or Frieren also forgot about Lugner, and was able to estimate how strong he was just with a look. Without using previous knowledge.
Frieren with a Dio voice:
"How many breads have you eaten in your life?" 