Yes. But their last 6 years' work has all be based on it having been made law that the number of constituencies would be 600, with every one being within 5% of 74,769 voters (except a few island exceptions). Those parameters are fixed by law.
In their own words - "The Commission wishes to make very clear that those with an interest in the review process should understand that the defined number of constituencies and the 5% electoral parity target are statutory requirements that it must apply and that it has absolutely no discretion in respect of either matter."
The allocation of wards to constituencies is the implementation/what will be voted on in September 2018
I read that as parameters that they must apply to their review, not that the review must then be applied by Parliament. "It" being the commission in that sentence, not the government/parliament.