Yes, I have noticed this a couple of times when reviewing My Devices.
If you choose to click on one of the Devices, more info will appear. The times I experienced this, the glitch seemed to be in the syncing of information between Device/PC and Avast program.
For me it cleared up.
You can Check the "Security Information" of each Device just to make sure.
Edit: Interestingly, I just noticed that the Information the Avast software has accumulated relating to the HP Laptop (Screenshot) is incorrect in that it shows OS as Windows 8 however my OS is Windows 8.1