The events from vBCredits do not directly correlate to the activity types in vBActivity. They are two separate systems that do their own calculations.
For example, one may not consider soft-deleted posts while the other one does, plus there are actions in one not present in the other.
As Fillip H. explained, vBActivity is concerned with measuring activity, and the exposed points for use as a currency is merely as a courtesy for those looking for basic integration; but since you are using vBCredits, I recommend just using that specifically for your currency needs because it was built for that, and leaving vBActivity to keep its measurement for itself.
Now, if you are trying to use a single point type across the whole site, you can use vBActivity's points within vBCredits, but then you have to leave the vBActivity actions to vBActivity only, and any supplements done by vBCredits may skew the calculations in vBActivity, because again vBActivity is using its point field for measurement.