The basis of this discussion begins with definition of both of these terms. Abstractive art is art that derives some or all of it’s composition from examples from reality. Abstract art is not bound by these constraints and may have no basis at all in the real visionary world.
I feel that many of the cave paintings and the Bison appear to be more abstractive rather than abstract. There are reasons why they appear more abstract. The artists were working with the skills and materials that were available at that time. They were restricted by their lack of understanding of linear perspective. The first linear perspective was used by Fillipo Brunelleshi and was first painted in 1415 A.D. It depicted the Baptistery in Florence. The artist did try to convey a sense of perspective by displaying the animals from two different perspective a side view and a front view depicting the head and horns of the animals. Without linear perspective the depictions appear to be flat or more abstract. In these cases the abstract appearance comes from the artist lack of skills that would not be available for thousands of years.
There were also some social/political reasons for denying the authenticity of these drawings and to question the timeline. In the movie, Finding Altimaria, (2016), Directed by Hugh Hudson, the Spanish Catholic Church is depicted as wanting to deny both the timeline and authenticity of these drawings. Their existence brought concerns about the dogma associated with the Catholic creation stories. By denying their timeline the church was able to cast doubt on what they represented. They considered these depictions as more abstract and not abstract