Whole lot of "if's" here.
I take it this is an apartment building, so I'm going under that assumption.
Talk to some of the tenants if you can - ask them if they've had any breathing problems. If so? Move on.
Find out why they had the mold, and when. Couple of years ago? Probably okay. Couple of months ago? Alert.
Find out WHO did the mold remediation work. You say you were told the mold was "treated". How, is the question. If the mold was in the walls (not on the walls), most likely a mold remediation company would've come in and taken the drywall off and attacked the mold there. Fix it, re drywall, paint, etc.
If the "treatment" was wiping the walls down with bleach water or some such concoction, and IF the mold was IN the walls, what they did would be akin to putting a band aid on skin cancer. They hid it.
Were any other units affected, if so, they were also stripped down and fixed, right?
What I'm getting at is, if the mold was actually IN the wall/walls - it would've been a huge fix, dollars wise. A true mold remediation company would have sealed that apartment/those apartments off with plastic, used an air filtration system while the tore the drywall off - the workers would've been in plastic suits with air masks, etc.
And, lastly - not all mold is necessarily toxic. Do you have kids?
JMO - I am NOT an expert.