It's likely an automatic email, or even an attachment to your invoice/packing slip.
Since Detailed Seller Ratings and feedback are no longer part of a Seller's account rating, the note is just a leftover from the days when feedback was important.
There are lots of problems in the world. This is slightly lower than a mosquito bite.
This seller then will block you from bidding because you did not give them a 5 star rating.
Well, you lucked out there. A seller who is spending the time to work out who is not leaving unimportant ratings is not concentrating on his real business. Not someone you want to give your money to.