The emphasis on OP's quoted line should be on _technically_.
A bill has to proceed through Royal Assent by the Queen before it becomes law [1]. It just happens that she is always timely with this duty and always agrees with Parliament.
Also the government's executive power is primarily through Royal prerogative [2]. _technically_ the Queen could exercise these powers herself for her own benefit.
The "checks and balances" that keep the Monarch from abusing these powers are a combination of tradition, facing the wrath of the British people and precedent set by what happened last time a monarch attempted to abuse royal prerogative [3]