Has your main point of contact changed ?
This unique sequence of events does not include an assistant putting a meeting on the calendar with the main point of contact nor it refers to a deal that has been openly promoted, bottom-up style, in your prospect’s organization. This case refers to a more "subtle" shift or responsibility or a soft handoff from the previous point of contact to a new one.
What might have happened?
(a) You were silently "downgraded" to speak to someone with a lower social rank than the previous, i.e. your previous point of contact figured it would be more convenient to put you in touch with someone more junior in the organization.
(b) This can also imply that the roles in the organization you're facing are less structured. This can turn out to be something positive. A "flat" organization means more people hold decision-making power and (potentially) shorter sales cycles.