Well, I have seen first hand the recoil political parties can take when they make promises that they can't (or won't) keep.
Dude's party by all accounts is heading for a landslide victory already.
Exactly so he has nothing to worry about, and can say whatever he likes. Interesting that he chooses to say this thing in this way. Tells me something about how he plans to run things.
He plans to run things as a center or light center-left. That... was hardly a secret even to me a full ocean and a half away.
Dunno why it would be a surprise to anyone, honestly.
The US "center" is very right-wing by international standards. By British standards, Starmer is very much centre-right. He's basically David Cameron without the aristocratic lineage.