I hope so. But it's neither a fact nor sound.And regardless of the accuracy of the first statement, the conclusion made is sound. i.e. With that amount of money this is a major piece of content.
This advanced payment is mostly refundable and covers exclusivity rights. So God knows what DLC size will be.
Even ignoring most of those, it may simply be a $10 DLC with expected 5 mega downloads.
There are other issues with big DLCs. For example, a next gen Vice City equivalent may anger retailers if it doesn't show up as disk soon. From Rockstar's point of view too it doesn't seem to be a sound deal at all, since disc iterations have been proven to be very successful, way too hard to skip.
Not to mention all those complaints from 360 owners about Capcom install sizes on PS3.
Again I hope GTA DLC for 360 is significant but that blogger is a plain tool.