Tantashev initially waved play on after Desire Doue went down under Diego Gomez’s challenge, but changed his mind after he was summoned to the VAR monitor.
"I saw it at the VAR screen when they were looking at it," Alfaro said. “I was behind the referee, and I cannot be objective.
"The referee has a first impression. He says that the player had thrown (himself) trying to generate contact. Then VAR ratifies that it is a penalty, according to them.
"I'm going to look at it more in depth. And when I am looking at the game play, of course, he's in the air, he's very skilful, and he can move in that small space."
Alfaro had insisted before the game that what his squad achieved was exceptional.
His nation will likely agree and Paraguay President Santiago Pena declared Tuesday a national holiday after their shock win on penalties over Germany in the round of 32.
But he conceded the end of the tournament brought a conflict of emotions after coming so close against the twice world champions.
"I leave the World Cup with peace of mind knowing that we played," Alfaro said.
"I am sad because I wanted to go further and defeat will never make you happy, of course.”
"I do not like losing at anything. And as I was telling the team in the dressing room, if you want to be a winner, the first thing you have to do is learn how to lose.”
With Alfaro’s contract up at the end of the year, the 63-year-old Argentine who has managed the bulk of his career in his home nation's domestic league said he was unsure of his future. But he clearly holds a deep appreciation for his adopted country.
"Today I have open wounds. I'm bleeding. I cannot really reflect because I am overwhelmed right now. I think I need to wait for things to calm down,” Alfaro said.
"Things need to calm down and we'll see what happens. I honestly do not know what I'll do professionally.
"For me, there's no better place than Paraguay. The country has opened up their doors, clubs have opened up their doors, the relationship I have with players, the relationship of gratitude I have with everyone."