I'm going to go ahead and play the devil's advocate a little bit here. The company that built the pond, MAL Zrt, appears to be a fairly small local corporation.
Website It is not inconceivable that something like this could happen to a small company without the expertise to build a containment pond to international standards and without the funds to hire a consulting company to do it for them, in a country where government oversight might not be the greatest either. Interestingly, the article does not mention what triggered the breakout - my guess would be heavy precipitation.
Was this caused by corporate greed? Maybe, in part. Was it caused by stupidity, human error, and the failure to design for extraordinary circumstances? Most likely that played an important role as well. At this point, not a ton of information is available.
Corporate greed is when you have a situation where a company repeatedly IGNORED safe practice because it would be more expensive, when they easily had the funds and damn well knew better, like the Exxon Valdez or BP oil spills.