Meaning of "sound hard"

Dear teachers,

I read a news article, and saw an expression "sound hard."

I wonder if this expression is natural to the eyes of the native speakers.

(1) The intention of the writer is not "sounds difficult to understand," but "it reminds us of something stiff and not soft."

(2) Please refer to the following article which I read for your reference:

http://world.kbs.co.kr/english/program/program_economysmall_detail.htm?no=10068815

Plastic injection molding may sound hard, but this mask is made of plastic that’s very soft, harmless and eco-friendly. It’s made with the same material that’s used to make the urethane tube in syringes or babies’ teething toys. The mask that I’ve developed comes with replaceable filters.

Hope to hear from you soon.

David Kim