The find was real enough, carried out by legitimate researchers and properly presented to the archaeological community for consideration. The first analysis did include what *appeared to be* evidence of cocaine as well as nicotine (they also mentioned evidence of cannabis, but that is hardly remarkable for the Old World at the time); a follow-up study found only the nicotine. Obviously there are some serious questions...starting with the possibility of modern contamination. It is also possible that the testing method could have identified similar, but not identical, compounds as "nicotine" and "cocaine". There are some issues with the concept of a detectable level of THC still present between the time of mummification and the time of testing, as well, which casts a certain doubt on the accuracy of the test and/or the methods of interpretation. However, the same testing and interpretive methods have not been challenged in regards to their demonstration of, say, arsenic in Napoleon's body, or laudanum in Keats'.
There are a couple of nicotine-
containing plants which are native to the Old World, including, of all things, celery (I believe all of the nightshade family, some members of which were used in Egypt, also contain a degree of nicotine). So nicotine present, even if the testing was 100% accurate, does not necessarily imply tobacco. Fake mummies, made from 19th-century corpses, were also not exactly uncommon and would tidily explain both nicotine and cocaine - though it seems unlikely that all nine of the tested mummies were fakes.
The main problem with many of the discussions on this topic is that their primary point is, "the researcher could not have found what she appears to have found, because we do not believe there was contact between the Old World and the New World at this time". A number of good careers in archaeology have been destroyed by the doctrine of, "this find cannot possibly prove what it seems to prove because we don't believe it is possible" - "Clovis First", for a long time an absolute doctrine that no one who wanted to continue working in the field would dare to challenge, has recently been rather thoroughly disproven.
A good follow-up summary of the investigation, the testing methods, the problems raised by various critics, etc., can be found here:
http://www.faculty.ucr.edu/~legneref/ethnic/mummy.htm
I think this is a bit of "extraordinary claims require extraordinary proofs" here...which may not be a valid scientific approach, as "extraordinary claim" is, ultimately, an OPINION based on....er, based on the opinion of the community and the individual researcher, often enforced by withdrawal or denial of things like jobs and funding if the proposition does not fit the current doctrine.