What does IEO mean?
A little bit out of topic, but... Initial Exchange Offering, in a way it's similar to ICO in sense of purpose; that is to gather funds for a project.
The difference is, on ICO, you can't be really sure if the team will really launch the project or not, given that you basically send funds to one designated wallet created by one "unknown" entity, and you can't be really sure about what'll the team do after ICO ends, there's no guarantee that your investment will not disappear (in short, you can't be sure if a project is scam or not).
On IEO, an exchange host the event, you'll need to have an account to the said exchange to be able to participate. The positive side of IEO is, as an exchange will have a tendency to be wanting to maintain their reputation (hosting a scam project's funding definitely will not look good on their resume), reputable exchange will likely verify the project's legitimacy up to certain degree that the possibility of a scam can be somewhat minimized.
In a very short: IEO is a more secure ICO held on an exchange.
So, at what exchange should Matchbillion where listed? I hope they were listed on big volume exchange even though not too much well known. Well, let's wait for the official announcement it here by the team and dev.