They hired a former dev, guinsoo. At the time when LoL was announced dota was being developed by icefrog for a few good solid years already. Most of dota's popularity happened during icefrog's years. Icefrog later joined valve and helped create Dora 2.

And some hijacking of the old DotA forums to advertise LoL: https://news.ycombinator.com/item?id=13439036