«وَقَدْ صَرَّحَ الْجُمْهُورُ بِتَقْدِيمِ صَحِيحِ الْبُخَارِيِّ فِي الصِّحَّةِ»
The majority of scholars explicitly preferred Sahih al-Bukhari in overall authenticity.
This does not negate Imam Muslim's expertise or the general authenticity of his collection. The distinction concerns relative degrees of strength, not a dichotomy in which one collection is accepted and the other rejected.
Care in transmission criteria, chain analysis, and the aggregate of hadith-critical judgments inform the preference. A particular report may nonetheless have independent evidence that justifies a different ranking in that case.