[7bit]

A steep learning curve mean you learn a lot (y-axis) in a short time (y-axis). So the graph goes up fast (steep).

When making bold clickbaity claims like the author does, at least get your terms right...

[MattPalmer1086]

No, the phrase a "steep learning curve" implies that learning is difficult and therefore progress may be slow.

It is actually a misnomer. Your interpretation of the graph is correct, but the phrase actually means the opposite.