The £5000 was part of a much larger sum allocated for targeted Facebook ads, and they had authority to place these ads. What they did was certainly dishonest and should cost them their job, but it's hardly illegal to use the wrong targeting rules.

I would expect it's easy to make the case of misappropriation when directing the money to an unauthorized advertising campaign; or to an authorized campaign, but for a different, unauthorized product.

It's a lot harder to make that case here, with campaigns using unexpected copywritting and targeting, both of which were at the liberty of the people running the campaigns. Selecting those was literally their job and given the massive Labour gains, it's hard to argue they failed at it.

It's clearly a case of internal insubordination and disciplinary action - which I'm sure the perpetrators were expecting, but deemed them an acceptable sacrifice to protect the party from what they seen as the bumbling fools running it.