Simply hosting it with your information in would not have any such effect, but many commercial entities avoid anything xGPL just-in-case. In this case perhaps because they see a time that they might later want to package and distribute documentation that is in the wiki without converting it to something else first.
There is an extra concern with AGPL that does not exist with GPL specifically because of its key difference. AGPL applies to hosting the software and making it available not just distributing a compiled form. Some interpret this as meaning that if it is hosted on the same server, or in the same site, as other software then that other software becomes AGPL licensed too. I doubt anyone would enforce this interpretation but the possibility is enough to put off those who create proprietary software.
> making it accessible to the public that the copyleft license would then apply to my proprietary software?
Not just the public. Anyone you give access to, so for non-public hosted proprietary software you could be beholden to giving them access to the code under the AGPL in situations where AGPL applies. This will be a complete blocked for many creators of proprietary, or other non-*GPL licensed, software.
[if the above makes me sound against AGPL rest assured that I am not - I in fact might end up using it at least initially (at least until I decide upon which of the more proprietary-friendly options to use) for some near-future projects]
