This is an interesting question. It illustrates the sometimes perplexing flexibility of English. Oxford Dictionaries online provides a host of example of this usage. I have used most of them, so that the usage can settle in.
The pattern is for the verb (used intransitively) to be followed by an adjectival complement.
Convey a specified impression when heard.
- ‘My heart sank when I heard how happy she sounded.’
- ‘This time she said it louder, sounding genuinely confused.’
- ‘I thought entirely out loud and probably sounded quite crazy.’
- ‘I record phrases that I use often and playback to hear how I may sound to others when I say them.’
- ‘She didn't sound that pleased to hear from him.’
- ‘I had some difficulty deciding on a starter as they all sounded so tempting.’
- ‘I like that he always sounds happy to hear from me, even for a short call about nothing.’
This type of usage is common with verbs of sensation:
To look: The house looks dirty/stylish; Your draft proposal looks strong
To feel: Your way of saying this feels a bit weak
To smell: Their offer smells fishy to me.
You could call the formulation as in a sense metaphorical: using expressions of sensation to represent our understanding of what is said or written.