I use the bang commands, especially !gm for google maps and !gi for google images, on occasion, but I doubt Avast is responding to anything I'm typing in. It warns me before I even type in a search term, and if I recall correctly, just when the browser (with DDG) is initially brought up. (I'm generally on Firefox, but use Chrome on an limited basis.)
But the bang commands is a very plausible reason Avast complains, even though anyone using them clearly learns you 'leave' DDG - that's the intent after all.
Still wish I could 'train' my instance of Avast to remain cool.