It seems likely a carrier was present. SH X doesn't seem like a series where the AI has been given certain advantages to provide an added challenge, like randomly spawning craft or extended range.
And I think I encountered a carrier's aircraft as well when I was between Scotland and Norway, being closer to the Norwegian coast. A few separate flights of Torpedo Swordfish appeared near me, circled, and headed back in the same direction. Alas, my heading slightly south of their departing path did not reveal a carrier.
