(The move is called Tatsumaki senpuukyaku. Or just ‘tatsu’ for short)
You can use a “late crouch tech” to defend against such simple mixups. Block the tatsu, and after it’s done, wait just a little bit, and while still crouching, hit lp+lk (throw). What happens is, if they mash dp after the tatsu, you haven’t yet hit any buttons and you’ll block normally (You’ll probably get a free punish. Don’t throw, do a combo.). If they throw, and you timed your inputs correctly (not too late) your own throw input will register during the tech window for the throw, and you’ll get a throw escape. If they do nothing but block, you’ll get a crouching short (lk), and you can continue with a blockstring. (Though blockstrings are often unsafe against mashers. Just stop and block sometimes and watch them rise into the air in vain.)
Crouch teching is a very powerful defense, but not invincible. If your opponent delays their attack or the throw, or if you tech too early, the short will come out and get beaten during its startup frames. However, most dp mashers don’t really think enough to delay their attacks like this except by accident, so most of the time you will be able to defend against everything they do, and punish when they make a mistake.