Both the sideloader and Playdate OS recognize 1.1.2 as a separate app rather than an update to the previous version.
Viewing post in Version 1.1.2 Released comments
Yes. The BundleID is used to identify individual apps. I intentionally changed it in the hopes that this would resolve some of the folks who have been (so far) unable to install on their Playdate because they are getting an install error.
I understand this sucks and you'll have to manually delete the old app. Glad to hear you got 1.1.2 installed though :D