I got an egg from trade and it was nicknamed VENUSAUR.
Its discription said it would take a very long time to hatch.
When it finally hatched it was a level 55 female Venusaur.
Is this a glitch or something like it?
Well this is awkward, but it is obviously hacked because eggs can not be nicknamed and when eggs hatch they are their first evolution and is level 1.
EDIT: Some Pokemon aren't their first evolution when they hatch because they need special requirements. (e.g. Full Incense for Munchlax.) Thanks to Fizzcube for pointing this out.
There is a glitch where you can use the hp reducing berry on a Pokemon with 1 hp to make it faint when you have an egg in your party then you can battle with your egg you can even level it up and evolve it I don't know about the nickname though this will tell you more.
edit: this wouldnt be the case because it would be level 5.