These two are orthogonal. Simply put,

1. ABI is a set of rules for interaction between multiple code units (functions, translation units, libraries) running sequentially and calling each other, e.g. how arguments are passed to the functions, how return values are passed back, how exceptions are thrown and handled.

2. Memory model is a set of rules for interaction between multiple (potentially) concurrently running threads, e.g. how a compiler can reorder load/store instructions to main memory, which operations imply memory barriers.