The last logged on user will be stored in the database for every computer as soon as a logged on user was detected once during scanning. After that, this entry will only be changed if another user was detected during a later scan.
Likely the disabled user was logged on once while Lansweeper scanned the computer. After that, the computer wasn't scanned while any other user was logged on to it, so this information doesn't change on its asset page.
If you would like to remove this information, you could go to
Configuration\Database scripts, section
Database scripts and execute a command like the following. Replace the username with the user logon you would like to remove. We recommend performing a backup of your Lansweeper database before running a script here.
UPDATE tblAssets SET username = '', userdomain = ''
WHERE Assetname = 'AffectedComputername'