Per the article, the police visited the office to deliver a legal notice, not to investigate the office. In the United States legal notice MUST be delivered in person. It cannot be done over mail or email. I'd expect India is similar.
They had gone to raid the office, but since the Twitter team is working remotely due to Covid, the police couldn't find anyone in the office and changed the narrative to save their face.
Only one officer is enough to serve a notice. Why the horde?