The thing is they have to do him in. If they don't, the Commons will never have a PM ever again who will need to tell the truth or at least clarify the record. So really, intent doesn't matter. What matters his failure to correct it.
Or otherwise all Prime Ministers, Labour or otherwise will know they never have to bother.
Yes he lied. All they need to do is make that clear. He knows that: hence this charade. But it's to protect our system which depends on people having some integrity. If you don't have that then the Boris exception will apply to all.
All the kangaroo court stuff is for his supporters