It means that you can't unlock all the abilities with one character, which is probably why they give you 10-16 spots (I don't know which number has been confirmed.) Also, some higher level abilities, like Downed Fire and Lazarus Grenade are more than 1 point. Those 2, for instance, both have price tags of 5 credits and others are also 4,3,2,and, like you did say, 1 so not all the abilities are just one credit.
Those are rank 5, not five credits.
Rank 1 abilities you can pick up from the get go.
Rank 2 abilities unlocked at level 5
Rank 3 unlocked at level 10
Rank 4 unlocked at level 15
Rank 5 unlocked at level 20
I might be wrong with the level numbers, but it at least gives you an idea. All abilities are 1 credit, some are just locked until a higher level.