I have their camera system in my home (and am generally happy with it). You can set it to be accessible only via the local network (and whatever holes you punch through yourself, e.g. setting up VPN), but to compete with cloud-based solutions like Google Nest (if they haven't canceled that already), there is an option to make it available via unifi.ui.com also.
This isn't really cloud-hosted; but it provides a no-setup way to access your security cameras as if they were (as long as your UniFi device is online).
I'm assuming (but also trying to read more to verify) that this bug affected users who had enabled this option.
You can enable "remote access" (or maybe it's on by default, don't remember), that does something to allow remote access to your setup with your unifi account, probably tunnels it through unifi servers.
It's an option that definitely should not be in there, remote access should always be done via a VPN or something secure.
This isn't really cloud-hosted; but it provides a no-setup way to access your security cameras as if they were (as long as your UniFi device is online).
I'm assuming (but also trying to read more to verify) that this bug affected users who had enabled this option.