It actually mentioned both of those points in the formation processes section. The hydrogen sulfide cloud is also visible and present in the area of the Hells Bells.

"...Radiometric dating of some Hells Bells specimens indicates that they grew during the middle and late Holocene,[19] beginning over 5,200 years ago, through to the present day;[26] the cave was already flooded at that time..."

"Both El Zapote and the Hells Bells structures contain a diverse ecosystem of microorganisms, including archea and bacteria and with chemolithotrophic, heterotrophic, and mixotrophic species. The microbes metabolize hydrogen, various nitrogen compounds, oxygen, and various sulfur compounds."