By probing the population of binary black hole (BBH) mergers detected by LIGO-Virgo, we can infer properties about the underlying black hole formation channels. A mechanism known as pair-instability (PI) supernova is expected to prevent the formation of black holes from stellar collapse with mass greater than ∼40 - 65 M⊙ and less than ∼120 M⊙. Any BBH merger detected by LIGO-Virgo with a component black hole in this so-called PI mass gap likely originated from an alternative formation channel. Here, we firmly establish GW190521 as an outlier to the stellar-mass BBH population if the PI mass gap begins at or below 65 M⊙. In addition, for a PI lower boundary of 40 - 50 M⊙ , we find it unlikely that the remaining distribution of detected BBH events, excluding GW190521, is consistent with the stellar-mass BBH population.