This is not 2x matching. This is just plain and simple matching. You donate 50, they get a total of 100 - 50 from you, and 50 from the donor.
Yes, the total amount they receive is 2x, but the matched amount is 1x.
I sound pedantic but it's because this is in stark contrast to the Internet Archive's "3x matching" through the end of the month, in which if you donate 50 they receive a total of 200, because the matching amount is triple - 3x - what you donate.