Flickr explore is a fickle thing, I only shared it in a few groups.
Actually some people say you're more likely to get explored if you put it in fewer groups, but it's also down to number of views, comments and favourites.
If you put it into fewer groups but groups that have more people in them, then you'll get more views and more views will give more comments and favs.
My first explore was only in 11 groups, but some of those groups were quite large ones.
It's also down to what day and time you post it, which will mean either more or fewer people browsing flickr.
It's nice to make it onto explore, well done on the deer shot.
Liking your new 7D then?