He was writing to the people of Corinth, which was quite some distance from the Holy Land. Hell, people back then believed stories of dog-faced men in Africa and that one-eyed giants inhabited some of the islands of the Mediterranean.
The manticore was first described by the ancient Greek traveller Ctesias. He tells us that the manticore had a lion's body, human face and ears, three rows of sharp teeth in each jaw and poisoned spines in its tail, which it could shoot like a porcupine.
Oddly, I believe I've seen the same description used in these posts, but about each other, not manticores.
And we, who are so culturally sophisticated, know better?
Come on. Luke travelled a great distance to find out about what he had learned and wrote his Gospel to share the information. People could and did check out facts, as easily as people can and do today. They also could ignore them as easily as today.
Whether you believe what Paul wrote or not, Paul was putting the evidence on the table. And he was doing so for people who COULD check up on him, as we CAN NOT today.
Shalom.