A.I. is just another term that can mean almost anything as there is no definitive standard.
In much the same way Heuristics is bandied about by many AV, again there is no definitive standard.
Avast has two functions, DeepScreen and Hardened Mode, that could loosely fall into either category.
More is done to keep databases as small/efficient as possible. There are many signatures designed to detect different variants of a malware type, etc.