Being "denoted in dollars" means the returns are a specified number of dollars. Stocks, on the other hand, are "denoted in shares of the company" and the returns are the change in value of the company.
The share value is price x shares, so there’s an effective dollar numeraire.
It’s easy to imagine a well performing stock that neverless loses due to a currency shock. Indeed this is why one would typically hedge currency risk if trading a name outside of accounting currency
