Nothing in the dmg given is modified only extra dmg added post-facto this therefore was either you are just really bad or another amazing engine glitch on behalf of valve.

As for the thousands of extra dmg it deals as a % of what was done so f you dealt a lot it would deal out a lot. While I have some filtering in place I will be improving the code for this and other races in the future to ensure that dmg abilities can not be set off by the dmg ability itself to prevent any sort of stacking that may be occurring (note may as there is no signs that this is true as of yet)