No, we should not choose a different post for the tour because of the avatar
The people that look so close at the tour that they realize there is an icon that is similar to that of Reddit are likely not the people that will ignore everything else (plus the fact that it's obviously an avatar of some user) and try to use the site like Reddit.
At least that's what I believe. And I don't have any data to find out anything different. For example this extremely simple SEDE query searches for every comment that contains the word "thought" followed by the word "reddit" under the assumption that people would write something like "I though this site was like Reddit and I could simply get some feedback or start a discussion...", which only leads to one comment that is specifically about the difference between this site and Reddit. Everyone who reads this: feel free to play with the simple query by changing the text "%thought%reddit%" to something that you feel fits better (the "%" means "anything can be here" and it should all be lowercase for the search).
A quick look through the 97 results for "%reddit%" seems to suggest that people are quite often referring to Reddit. But never in a style that would suggest that they think that this site works like Reddit.
I don't see a problem. And a motto where I work is "If it ain't broken, don't fix it."
If you can find some data (even just a couple link to comments you have seen that show that people had this confusion) and suggest a better post I might be convinced that we should ask to change this. But currently I don't perceive this as a problem, I couldn't find evidence (granted, I only did a really short search) and I can't imagine too many problems arising from this, which is why I am saying:
No, we should not choose a different post for the tour because of the avatar.
Another thing to mention is that Rory has been quite persistent with his avatar as far as I can tell. I can't remember him changing his avatar in the time I have been here, which is different from quite a lot of people. I'd rather have this consistent user whose profile doesn't seem to be a big problem in the tour than having to regularly check if someone has changed his profile and is now having something weird.
I think I have flagged someone before for an inappropriate profile pic. In such a case we should change the post for the tour. But as long as you don't feel that you should flag a post from the user for moderator attention because of an inappropriate profile picture we should not ask to change this part of the tour.