As far as I can tell, mytreo.net doesn't have the right to distribute Opera Mini.
From Opera's Press Release
Opera Mini™ is available to end-users through operators and companies that choose to include it in their offerings to their customers. It is currently available as a pilot project through TV2 in Norway, with wider availability to be announced. For more information read the Opera Mini product page.
I think Mytreo.net's representation of Opera Mini as "freeware" is inaccurate and misleading and they are distributing the application without permission. Just because they managed to obtain a copy doesn't mean they can distribute it. If there's a EULA, it should accompany the download.