Yeah it looks just like the Windows SmartScreen message about brand new files that hasn't been seen before
As long as you downloaded the file from Aslain's own links, it's just a message to help you be careful (like if you actually downloaded something bad, it should warn you like that, just in case)
You can pick "I trust this file", it's similar to SmartScreen's message
And yeah, Avast probably did some update, if it's only recently you've started seeing it