I didn’t even mind the part with the water at the end; I thought it seemed believable enough. It’s not like the aliens were there to settle Earth, they were just an unknown threat present only for a brief time.
Let’s turn the tables around. If a group of humans were to visit a world – a world covered 71% with sulfuric acid, where it rains sulfuric acid, and where the native inhabitants have sulfuric acid on tap – and go down to the surface completely buck-naked with absolutely no protection from the elements whatsoever, would that be believable in the slightest?