Giant planets and brown dwarfs are thought to form via a combination of pathways, including bottom-up mechanisms in which gas is accreted onto a solid core and top-down mechanisms in which gas collapses directly into a gravitationally-bound object. One can distinguish the prevalence of these mechanisms using host star metallicities. Bottom-up formation thrives in metal-rich environments, whereas top-down formation is weakly dependent on ambient metal content. Using a hierarchical Bayesian model and the results of the California Legacy Survey, a low-bias and homogeneously analyzed radial velocity survey that detected dozens of planetary-mass companions between 1 and 10 au, we find evidence for a transition in the stellar metallicity distribution at a companion mass of M_t = 25.5 {+18.7} {-12.3} M_Jup. Companions below and above this threshold tend to orbit stars with higher and lower metallicities, respectively. In addition, we find that the two populations have distinct orbital eccentricity distributions, with the low-mass population more strongly preferring low-eccentricity orbits. We compare our results to other estimates of M_t made in recent years.