"Not as secure" means specifically this punts all the actual security of the system.
This is one of the sad but predictable thing with designs like WireGuard that themselves decided to punt this hard problem (you can also see it in OpenVPN [edited: Let's blame an early morning for me writing OpenSSL there] and with the same consequences). So in one sense it isn't your fault - Jason knew this was hard but left it for you to solve anyway, and predictably you didn't.
But of course for the end user the practical result is that they maybe don't get the security benefits they were told were available in WireGuard.
My crystal ball is cloudy but I'd guess that one possible future for WireGuard is that it gradually grows a reputation for insecurity not because WireGuard the protocol is bad but because the way it's used has meant almost invariably bad guys get private keys they shouldn't have.