I first heard of this theory from a Cracked article that mentioned cocaine and tobacco (which are New World plants) found in a pharaoh's tomb. Apparently there's lots of connections between the Aztecs and Egyptians, including that they both made pyramids, used hieroglyphics, and had similar religious beliefs. Now, I don't believe that Egyptians actually sailed to the New World (there's no records of it anywhere in Egypt, or in Mexico), but I was wondering why some historians believe that, or why that theory emerged.
No historians in academic circles take that seriously. So the answer is that, actually, historians don't believe there's any connection. Both Meso-Americans and Egyptians used "hieroghlyps", but they're actually unrelated signs of unrelated languages - we just refer to them as "hieroghlyps" because they're both visual depictions of words. Pyramids developed independtly too - why would that be surprising? It's not like it's a highly complex kind-of structure.
Source: the absence of academic sources (hah, never thought that would ever be a relevant answer).