Yes, that’s normal. That is the date that Infuse on that particular device last synced with iCloud. It only syncs when the app is active. If you launched Infuse on all devices on the same day and allowed it to complete an iCloud sync the dates would be the same.
Precisely, when I add content from dropbox at the same time on it’s different device, but the iCloud sync is very long on some device and the date does not move. Is it really stable to launch all the devices at the same time?