Who said anything about ‘constant’ acceleration?
“The accumulation can be additive at an increasing rate .”
Additive accumulation of displacement at a constant rate would be constant speed, and additive accumulation of displacement which is INCREASING at a constant rate is constant acceleration.
As well, you might have acceleration increasing with time which might give some displacement polynomial in time. So, there’s nothing about the quoted phrase which implies exponential increase, and I’m saying that constant acceleration satisfies the sense of it, in terms of displacement.
Exponential increase is defined uniquely by a rate of increase of a quantity which is proportional to the quantity itself.