Thanks, this is a known bug, fixed in version 6.16.
The definitions have actually been up-to-date all the time, only the date in the brackets is wrong. The important number is the first one - "190218" means that your latest virus def database was updated on 18/2/2019 (today).
Version 6.16 has been released to 100% of users by now, so you should be able to fix the problem by simply updating your Avast Mobile Security app.