That's true. Nevertheless I was talking about the war declaration by Asylon on Terran, almost simultaneous to the alliance between Aurvandil and Asylon. The war declaration places Terran in a delicate situation with two enemies really close. However, being Astrum and Iashalur allies of Terran, I guess they could offer some support in case of a direct threat from Asylon.
Aurvandil's got a really privileged geographical position. Falkirk seems to not be a filter to any attack from the east anymore, and maybe that pushed Aurvandil to seek another diplomatic advantage. I remember I read some time ago that alliances were some kind of dishonourable thing for Aurvandil, but I guess times and necessities change.