To put on my own nerd hat, the author is referencing "dat boi" as in "oh shit here come dat boi!" — not Pepe. Both are frog-related memes, but dat boi is much more recent and did originate on Tumblr, even if its final form may have actually come into fruition on Facebook — though Know Your Meme can be wildly inaccurate at times.

[1] http://knowyourmeme.com/memes/dat-boi

Ah got it, now I'm a bit embarrassed. I didn't even know that existed until a few weeks ago (a sign that I'm getting old?). Thanks for the clarification.