Why would you be assuming anything?
The only thing that was ever publicly announced was the dissolution of our shared faction tag.
?? With nothing formal saying their is a defensive alliance agreement or something similar, when I see a faction/alliance dissolve into separate factions (aka fimbrulvetyr, velucan empire, etc.), my first thought isn't "I wonder if they still have an alliance" - i usually try to stay on top of various alliances and wars and I had absolutely no fucking clue frisians had a defensive alliance still in place with ravens, so I can completely understand a new faction to strategus not knowing this. You didn't exactly break up on the friendliest of terms, something similar to what happened to VE - ad no one thought (thought correctly) those guys were allied afterwards either. A formal alliance with dracul was mentioned when you broke up but nothing about frisian defensive agreement.
To be fair - dracul declared war on acre and you are helping your allies - very valid reason for war and I wish you the best of luck and hope for some fun xp-filled battles - don't see any need to post any conveluted and elaborate reasoning related to frisians who you are no longer allies with as of our peace agreement with you. Draculs declare war - you are allies - end of roleplay no need to insult back and forth with each other (hell i would probably be insulting too if someone tried to say their alliance which ended 3 months ago with frisians required them to attack us now when frisians asked you to stay out of it 3 months ago and acre never attacked again).
Just keep it civil on both sides - dracul and ravens are allies fighting acre. END of story.