At the AGM the Owners Corporation, determines the number of members to go on the strata committee, and then asks for nominations to the committee. If the number of nominations is less than or equal to the number of members determined for the committee, then they become members of the committee (or otherwise there is an election, and the owners with the most votes form the committee). The office holders of the committee are not elected at the AGM, but at the first strata committee meeting following the AGM. That meeting often is called (with an agenda, with this as the main item) immediately after the AGM concludes.
Signing the strata managing agent agreement, involves affixing the Owners Corporation seal to the agreement. That is governed by section 273 of the Strata Schemes Management Act (& Reg 17A). For schemes with “more than 2 owners” the seal must be affixed in the presence of the secretary of the OC and any other member of the strata committee, or if there is no secretary, then in the presence of “2 persons, being owners of lots or members of the strata committee” that the OC determines for the purpose of signing that agreement.
Since your OC hadn’t determined any member to be the secretary, then 2 owners, or 2 committee members can sign the agreement, provided that is approved at the meeting, and so noted in the minutes, as being authorised by the meeting to do so.
There might be an issue if the 2 persons signing when the seal is affixed are co-owners of the same lot? But s.273 states the 2 persons need to be “owners of lots” (plural), or members of the strata committee. If they are co-owners of a single lot, then they may not be sufficient to sign and properly affix the OC seal.
But I wouldn’t stress about this. The main issue, is that the owners at the general meeting approved the appointment of the strata managing agents. If the seal isn’t properly affixed, that is more a problem for the strata managing agents – there is case law that says they will be the ones with the bigger problem if the seal isn’t correctly affixed on their agreement. (Their agreement might not be valid, and they might have to pay all the money back they were paid by the OC…)