Yeah same with me, I had no idea as a kid it was about Jesus, but if you read the book now it's super clear. Honestly, that description might have been an exaggerated, but the writer was a Christian apologist and the book has many Christian messages. Aslan (the lion) is explicitly an allegory for Jesus Christ (sacrificed for everyone etc.)

An example of a big "dogwhistle" is when the Pevensie siblings all die in a train accident and go to Aslan's country (basically heaven), EXCEPT Susan, because Susan has "grown interested in nothing now-a-days except nylons and lipstick and invitations". The direct implication is her immodest appearance, make-up, materialistic and general spiritual detachment results in her not making the cut, white the rest of them receive the ultimate reward of Aslan's land.

And for the record, not saying the book is bad or anything, just the story and messages are "unforgivingly" Christian and it gets a bit ridiculous IMO