Legality of redesigning/building client's website without permission

Saw this somewhat horrifying anecdote on LinkedIn, and I thought it has to be breaking some sort of law somewhere. Basically, a company had a web development agency build them a website, and presumably the latter managed the hosting for it.

However, the company later on wanted to 'test' their AI tooling and development process, so redesigned and rebuilt said company's website without permission using that process. This redesign ended up leaving incorrect information on the site, like outdated contact info and branding.

So, assuming an agency did actually do this, what laws would they have broken? Could the agency have had a contract that would allow them to do this?