Yes, they are wrong.
"The large expanses of olivine, about one-million square miles, means chemical weathering on Mars was very low and has been low for most of its geologic history. This information contradicts a popular view of a past warm, wet period in Mars' geologic history."
And what they don't tell you: that 1 million square miles only accounts for 2% of the Martian surface. Where is the olivine on the other 98%? Has volcanism not occurred on that other 98% of Mars? Of course it has.
Either that olivine has been weathered away by aqueous processes or that volcanism has been of another type such as andesitic volcanism, which is itself associated with high amounts of water in the volcanic lava.
Bob Clark