The statement you provided is incorrect. Time dilation refers to the difference in the passage of time between two observers in relative motion or different gravitational fields. It is a phenomenon predicted by Einstein's theory of relativity. However, the statement mistakenly assumes that time dilation would cause us to "be long gone" by the time an alien civilization reached us.
In reality, time dilation effects would only occur if there were significant differences in relative velocity or gravitational fields between the two parties. For example, if the alien civilization were traveling at a substantial fraction of the speed of light, then time dilation would indeed cause their time to pass slower compared to an observer on Earth. However, from their perspective, it would still take a certain amount of time to reach us, and they would observe time passing normally on Earth.
Likewise, if the alien civilization were coming from a significantly stronger gravitational field, time dilation would occur, but it wouldn't lead to us disappearing. Time dilation effects are relatively small in everyday circumstances and require extreme conditions to become significant.
Therefore, the statement fails to consider the limitations and magnitudes of time dilation effects and wrongly assumes that time dilation alone would cause us to vanish by the time aliens arrived.