We can't answer you as to exactly where it came from, but hairy bittercress is a plant that has great ability to move it's seed further every year by launching it far from the parent plant, and taking advantage of openings is the lawn and garden.
It is a winter annual, meaning it actually got started in late fall and was an unobtrusive, rather attractive rosette of green leaves all through the winter. (which is an easy time to pull/disrupt it). It becomes more noticeable as it grows tall, blooms and sets seed which is now.
Here is our page about it and best means to control: http://extension.umd.edu/hgic/topics/hairy-bittercress