Good question, Tobias. This is a pronunciation issue.
Āsēvana is different from asēvana.
Sēvana is association. Āsēvana (Ā + sēvana) is “came to associate with”.
On the other hand, Asēvana (A + sēvana) is “not to associate with”, the negation.
It is very important to see the difference, which illustrates how Pali words combine (sandhi) to produce other words with very different meanings.
P.S. I just added comments in the two posts, “Associations (Sēvana)- A Root Cause of Wrong Views” and “Āsēvana and Aññamañña Paccayā” to emphasize this point.