No, it looks like damaged, stained wood or wood product. Not all mold is dangerous or deadly so don't overreact. Show the landlord when you do a walk-thru before moving in.

Thank you for responding. I'm the owner. Do you have any recommendation on if I should treat or get it checked for it's mould? Thanks!

Scrub it with a toothbrush and something like barkeepers friend....even if it is mold that should take care of it.

Thank you @lindac92! I'll try that. I'm not sure what the cleaners tried using but they weren't able to get it off

Yes it’s mold. They created a moist environment with their plants which they likely overwatered occasionally. Spray it with bleach and let the area dry out. It may need to be repainted or refinished but if you don’t store plants there the mold won’t return.