The 19-year old forward, who is a Homegrown Player at the Galaxy, netted three goals in four appearances for the US U20s during their CONCACAF Championship campaign in which they lost the final to Mexico earlier in March.
"Just being able to be that go-to guy on the [US] team," said Villarreal.
"They kind of looked for me most of the time, so being able to help my team and be the one guy they looked to play just felt like a leader. Not a vocal leader, but just on-the-field performance-wise."
He added: "It was very tough (being away during preseason).
"In preseason, I knew there were potential spots to be taken. The time I was there, I think I took advantage of it. And it was another good experience to be with the U20s. Now that I'm here, I'm expecting to start of where I finished off the preseason and go from there, working hard."