If more than 50% of personal computers have 1 or 0 users, then the median would be 1, assuming 0 users is less common than 1, regardless of how many users the remaining computers had.

If more than (or equal to) half of computers are used by only one person, then the median user count is 1, no?

If you have 3 PCs in the world, one with 0 users, one with 1 user and one with 23 users the median is 1.

Median is literally the middle, like a highway.

They're just stating that having more than half of all computers with just 1 user guarantees that the median is 1.

No.

For example, suppose five computers have 1 user, 1 user, 1 user, 3 users, 300 users. The median is 1 user.

The claim of "median 1 user" just means more than half of computers has a single user.