The strata manager would be invited by the committee, acting as the owners corporation. The law (below) seems to suggest that the chairperson must chair the meeting if they are present.
However, the responsibilities of the chair, secretary and treasurer of the strata committee can be delegated from time to time to the strata manager, via their contract. That means that at any given time the AGM could have two chairs in attendance – the elected chair and the contracted chair, i.e. the strata manager.
Strata managers conducting general meetings is standard practice and its legitimacy is rarely challenged as the standard strata manager contract allows them to do so.
To answer your question about whether or not the majority of owners can challenge this, they could insist that the chairperson chairs the meeting, but if they didn’t want to and resigned (until the meeting was over) then it would fall to the strata manager anyway.
For your reference Section 12 of Schedule 1 of the Act says:
12 Chairing of meetings
(1) Chairperson to preside
The chairperson of the owners corporation is to preside at any meeting at which the chairperson is present.
(2) Presiding member where chairperson absent
In the chairperson’s absence from a meeting, the persons present at that meeting and entitled to vote on motions submitted at that meeting (other than unfinancial owners) may elect one of their number to preside at that meeting and the person so elected is, while so presiding, taken to be the chairperson of the owners corporation.
Section 13 of the Act spells out the duties that may be delegated to the strata manager, and these include conducting meetings.