It's hope for the best, prepare for the worst.
He's laying out what it will be like if infection controls work, and we can indeed be agile in quashing any little flare ups to prevent then becoming clusters, and prevent those clusters coalescing into a regional rise.
It's a kind of 'jam tomorrow' but it does depend on things like hand washing, use of masks, keeping 2m away from strangers (unless necessary and mitigated), high hygiene standards, and employers making good choices about Covid safety in the workplace.
But it's also preparing for the worst. Continuing high levels of PPE purchase, further buttressing of test and trace, expanded flu vaccination programme, retain the Nightingales, powers to local councils (who have responsibility for local Public Health) to impose targeted lockdowns etc
We don't know how it will go over the autumn. Implicit in the research that SARS-COV2 is milder in hotter weather is that it is more readily transmitted in cooler weather. It's not gone away, and we are seeing that it can spring back quickly.
So yes it might all go pear shaped.
But we don't know that it will, so we might as well be optimistic that we am get it right.