It’s not unique to your app. It seems flathub.org occasionally falls behind in pulling the latest versions. It is not the first time this has happened. However, my distro’s app center usually displays the latest release.
I think users will install the latest version but for some reason flathub.org is still displaying the old version. Even running flatpak remote-info flathub com.heroicgameslauncher.hgl pulls the latest version. The issue must be specifically with flahub.org’s frontend pulling this information.
I experienced the exact same thing some time back. Check this thread.