It's very 70's in writing style.
You can tell a lot of the writer's of the era were frustrated novelists.
So they used captions. So they can feel like they are writing at least a novella.
They used captions A LOT. Mcgregor would describe what Tchalla is doing in a caption while we can clearly see what he's doing because there's an artist (Billy Graham in this case, if I remember correctly) who drew the scene. But that wasn't going to stop Mcgregor from getting his novella on.
It's wasn't just him, tho. A bunch of the writers that got big in the 70's did that kind of thing. Mcgregor, Englehart, Steve Gerber. Even Marv WolfMan ( the Teen Titans guy) used that style when he was writing Tomb of Dracula.
At least he only used that style when story called for it.
The other guys....?
It's ironic that Chris Clairmont was probably the last star writer from that era but he hung on to caption over writing to this day.