Thank you for the question. In researching my answer to your question, I found out that Nyger seed Guizotia abyssinica  (also known as Niger, Nyjer, and other names) is often sold or referred to as thistle seed as a marketing tool to get people to buy it for finches because finches love thistle seed, but it is not a thistle.

Guizotia abyssinica and common thistles are from the aster family but Guizotia abyssinica  is closely related to the sunflower. It can grow to 0.5-1.5 meters tall and has yellow flowers, and is an important cooking oil crop. It is an annual plant meaning that the plant only survives one growing season in Minnesota. Most seed is imported from Africa or India and must be heat treated to reduce the chance that noxious weeds that might be "riding along" become invasive here and it keeps the nyjer seed from germinating but preserves its nutrition for birds. The University of Purdue Horticulture department states that " Arguing against its weed potential are the facts that it is a short day plant, self-sterile, and requiring bees for pollination". Short day plant means that it requires daylight of less than 12 hours to flower. Our days are much longer than this during the growing season, so I think the chance of the seed sprouting in your lawn and surviving to produce flowers and then seed, are quite low.

Here is the Purdue publication: http://www.hort.purdue.edu/newcrop/duke_energy/Guizotia_abyssinica.html

Here is a University of Illinois Extension commenting on the seed: https://web.extension.illinois.edu/cfiv/homeowners/990925.html

Thank you for the question.