DESCRIPTION
This kind of joke is what we call "low hanging fruit" or a "red meat" joke. It means it's going to be popular towards the audience you are making it for. In this case, internet folk! They all know the kind of weird stuff that happens involving tentacles. Needless to say, this episode was VERY popular.
It also showed us that Twilight does plenty of kind gesture's such as helping Apple Bloom with her report and checking for errors. What a nice thing to do.