I used to live and work in this part of London. It's suburban, but it's not all posh and wealthy by any means. Not everyone there works in the City, and there's a fair proportion of stretched lower and middle income people and families who rely on having a car and can't afford to just replace it. It's definitively not like central London in terms of demographics or density of public transport.
Extending ULEZ is a sound concept, but to try to enforce it without adequate support when so many are struggling is always going to result in resistance and Labour can probably expect to get punished for it again in similar parts of outer London.
Combine that with a Labour party that offered no positive reason to vote for them beyond, "we're not Tories", and it's not surprising that the local issue caught the voters attention.
I don't think the result will worry Labour overly, and what you saw from Starmer here (i.e. fuck all), is what you'll see going forward. A policy vacuum, an empty husk, a man who's outstanding talent is not wearing a blue tie. I suspect that has a limited shelf life if he gets in power...