Best guess on this is Sisu spoke to Sinclaire, who said State Aid (she did say she was advising on EU law). I'm not sure I'd trust Sinclaire's judgement on the finer points of EU law as an anti-EU MEP, and I'm not sure that Sisu only take cases they will win. The bringing of a case is an ends in itself, it will cost, gag on side in the PR war, etc.
From my reading of the State Aid laws, I can't see how they have a case. The argument seems to have to be that unfair competition was created by the aid (as well as the caveats OSB has posted) and I'm not sure you could seriously argue that Sisu are in competition with ACL, but it will be interesting to see how it plays out.
On topic: This request seems to me to be another mudslinging attempt. Go through the meeting minutes, pick out anything that can be attached to a councillor and smear them. That's been their modus operandi so far any way. I'm not sure democracy is best served by those means TBH, at some point people have to be able to speak freely in meetings and what matters is the overall decision taken, not the arguments along the way. But as I said, it will be interesting to see what plays out, I'm still not convinced Sisu are the silent assassins they are made out to be, more deranged mugger with a shotgun.