imgflip is very commonly used to make memes (what I recommend on my site, I actually redirect ppl to it with my create a meme icon), so the imgflip watermark is very common on memes n doesnt necessarily prove anything. a direct link to its creation on imgflip helps but the issue is that someone else has already made that meme previously regardless the OC concern. I would just recommend to stopping worry about that one single meme and make another, chances of ya duplicating a meme someone else has already made before twice in a row is pretty slim.