Working from a rough estimate of what the embedded option is worth (~55-65 million on $600 million principal or 9-11%) the convert buyers are effectively taking on the senior debt credit risk at 3.5-4% YTM or a 270-320bp spread to 5-yr treasury.
from a textbook standpoint you are correct. however in an adverse scenario the conversion option will be worthless anyway. the simple yield would be the end result in that case. to loan money to a company that posted a (meager) profit just once in its 10 year history at 1.5% is just plain dumb imo.