This, if I understand you, is the way I read it.
You're reading it wrong.
A surprised creature can take no actions (nor can it move) on its first turn (during round one) but once that first turn ends, it can take reactions normally.
Example:
A 5th level Monk (Dex 16) is surprised by a
hidden Orc Archer who has just declared a crossbow attack at the Monk, triggering initiative (
before any attack rolls are made). The DM calls for initiative.
The Monk rolls a 15 for initiative, the Orc rolls a 10.
Round 1 starts:
The Monk has his first
turn. He is surprised and can take no actions or move. His turn ends. He can now take reactions.
The Orc has his first
turn. He uses the Attack action to resolve his attack with his crossbow. He has advantage on his attack roll on account of being hidden, and rolls the d20 twice, hitting the Monk (and revealing himself). He deals 1d10+2 (the Orcs Dex mod) damage for a total of 8 points of piercing damage.
The Monk uses Defect Missiles class feature as his
reaction. (At the last second his awesome monkiness and super dexterity kick in like a bad-ass as his hand snaps out like lightning to catch the bolt like Mr Myagi catching flies with chopsticks). He reduces the crossbow damage by 1d10+8 (his monk level plus Dex mod).
In this case he reduces the damage to 0, so as part of the same reaction, he also spends a Ki point and hurls the bolt back at the Orc like a total boss. He hits the Orc dealing 1d6+3 (the crossbow bolt is now a Monk weapon) points of damage to the Orc.
The Orc wants to go back into hiding, but cant as he has already used his action so he cant take the Hide action. He instead uses his movement to duck behind total cover.
Round 1 ends.
Note that the Monk has now spent all of six seconds standing around like an idiot, taking no actions or moving. This is because he was surprised (caught with his pants down) on round one, allowing the free Orc to get a shot off at him.
He was however quick enough to use a reaction in response to the attack (determined by the opposed Dexterity check vs the Orc at the start of the combat called 'initiative'), and due to being a Monk, he also happened to have an applicable reaction to take (deflect missiles).