According to Pearsons hard soft [Lewis] acid base principle, hard Lewis acids have a strong affinity for hard Lewis bases and soft Lewis acids have a strong affinity for soft Lewis bases. beta-Propiolactone reacts with hard nucleophiles (such as HO-) by acylation, and soft nucleophiles by alkylation.
Note that while hard vs soft comparisons can be made for carefully selected pairs of species and/or reactive centres, the HSAB analysis is NOT general. For more information look in the Chemogenesis
webbook section on Pearson's