You can't tell faring from the number of tickets. And I'm not even sure that UA even passes through the underlying fare information the way that Lux Flyer indicates, nor is it clear why A3 would be bound by it if they did. There's no guidance for mixed-cabin, mixed-carrier flights -- the IATA doesn't say what to do; the DOT doesn't say what to do; it's just never considered, All we can say is that A3's policy holds, but we don't know which policy -- short-haul economy, short-haul business, long-haul economy, long-haul business; I could make a coherent argument for any of them.

If the receipt says €90, it's fair to say that you'd be charged no more than €90. Whether you'd get a free bag, or whatever A3's short-haul bag fee might be, is up in the air. You might actually have more luck asking in the A3 forum.