Over the last few decades there have been massive improvements on telling which bones have attachment points for muscles and hints at how strong the muscles are likely to be, but it takes a long time to replace all of the existing artwork with newer and more accurate artwork.

Even with improvements to the muscle structure, any part of the body that has fatty buildup like breasts would be missed without soft tissues being preserved. I am fairly certain that a hippos nose and lip area wouldn't have enough detail to reconstruct accurately. Heck, tyrannosaurs most likely had lips to cover their teeth, but that is based on other animals with similar teeth all having lips to protect the teeth from dryness and rot that doesn't apply to crocodiles who live in a very wet environment.

As another idiot, there is a difference between tusks and teeth. They are different, tusks don't contain enamel for example and I think aliens could also determine this difference. It's rare for teeth to stick out like in the reconstruction.

They would also be able to determine that hippos can open their mouth extremely wide. Making it more likely for the long "fangs" to be at least partially covered and not exposed like the tusks of elephants.

I'll be honest, I double-checked your username to make sure I'm not going to read about Undertaker at the end