Increased ranking from spam attack?

This is a strange one that I am trying to figure out. One of my competitor's website received "negative" spam backlinks to their website. There was thousands of backlinks in a two week span. The backlinks were mainly from random sites with the anchor tags selling adult stuff The DR of these backlinks were ranging from 30-70. After this, the website's organic traffic greatly increased (over 100x).

How is this possible???

Thanks.

I guess that your competitor is having a freebie marketing campaign through those spam links, lol. Actually, those contextual links, even though they could be spammy links, do pass some link juice, and when you build those in thousands, it does help in the short run, but once google updates their algorithm all too often, that could translate to a lower ranking in the process after that.