Have you ever gotten an exact match?
if by "exact match" you mean "100% of the letters in this post match 100% of an organism's entire genome," then the chances of that happening by pure accident are so ridiculously small, you'd have better odds buying 100 lottery tickets and winning all of them!
one of the cool reasons this blog works in any capacity is because genomes are so ridiculously big that the chances of a random string of letters accidentally matching part of one is very high. the human genome is ~3,200,000,000 base pairs (or "letters") long. that's about 1,000 times the length of the entire bible. pretty long for a tumblr post!
but even in the case of the smallest possible genomes, such as bacterial endosymbionts (famous for having tiny genomes) with only 100,000 base pairs, it'd still be practically impossible. you'd need to accidentally type the letters a, t, c, and g in the correct sequence 100,000 times to get a perfect match. imagine flipping 100,000 coins and getting heads on all of them. ok now imagine a cat named big boobs