WILL IT BE AN INVASION?
The simple answer is yes. Even one alien stepping foot on Earth is an invasion. Unless they observe strict anti-contamination protocols (a bio-suit for example), their mere presence as a physical person brings along all of the microscopic creatures which have colonized in and on their person. Even one of these creatures residing in/on the alien could be deadly dangerous to us. It could be that the Earth’s biosphere is constantly bombarded with alien lifeforms through meteor and micro-meteor impacts and has the ability to adapt and defend itself (some think tardigrades could be alien lifeforms) and an alien visit wouldn’t be such a threat after all. We won’t know until it happens. There is zero publicly available evidence that any alien civilization visiting Earth has any military attack planned. If they’re doing reconnaissance for such an attack, they are clearly in no hurry – maybe it costs too much.