A screenshot of the this might help, as the icon should indicate if it is Avast or another program.
However, in task manager you should be able right click on the items Properties and see the location. This should also give an indication of the program and location.
Ordinarily when you install another Antivirus program Windows disables the Windows Defender on-access antivirus. This may not be true of other 3rd party anti-malware.
I’m using Windows 10, but it should be similar. When you go to your Windows Security area and then were your antivirus settings are (Mine says Virus & Threat protection), and then scroll down, do you see something that shows something about periodic scanning, like this
No worries, I thought it was that based on you having Avast and that Defender was running in the background but “only” using about 130 MB of RAM.
You can still have Defender running as a “second opinion” scanner that does a quick scan every once in a while, which is why it was running in the background. But the real time scanning is still off and won’t interfere with Avast or whatever third party AV you had installed. It uses more RAM when your computer first turns on and if it’s doing a scan or definitions update.
Mine for example is only using 4 MB of RAM as nothing is happening