After he did a double take, of course.
Escorting Mack into the room, Raiders college scout Raleigh McKenzie. Awaiting Mack inside the room, McKenzie's identical twin, Raiders general manager Reggie McKenzie. And yes, Mack thought it was the GM who had been taking such a keen interest in him all along, rather than watching from afar.
They all had a laugh, until someone on the Raiders staff asked Mack about his earliest NFL memory as a fan.
Mack, who grew up in Fort Pierce, Florida, told the gathering he remembered his home state Tampa Bay Buccaneers beating up on some team in the Super Bowl.
Yes, that Super Bowl. The one in which Jon Gruden's team thumped the Raiders 48-21 on Jan. 26, 2003, a loss from which Oakland has yet to fully recover, let alone have a winning season or playoff appearance since.
It appeared as though Mack, who set an NCAA record for forced fumbles in his college career at Buffalo, had fumbled the ball himself by insulting his hosts, as unintentional as it was funny.
"I was going to tell him, 'OK, you're in the wrong room,'” Reggie McKenzie said with a grin.
Instead, nerves were calmed.
"We started laughing," Mack recalled. "That speaks for what type of people they are in this building -- great people, some of the best. I'm glad to be a part of this great organization."
It's one that is expecting him to be a part of its turnaround. And it began not only with the Raiders selecting Mack with the No. 5 overall pick, despite never bringing him out for an official visit, but with Mack signing his contract Thursday, a day before the start of this weekend's rookie minicamp.
It showed that Mack, who will wear No. 52, is serious about getting to work and not letting the prospect of contract haggling overshadow his preparation.
"Coming to the professional level, I know guys are going to be just as talented if not more talented than I am," Mack said last week. "There are certain things that you have to do as a football player to make sure that you play fundamentally sound and use the right technique and play with your hands and do it every day and do it every time you go on the field and be consistent.
"That's what I'm looking forward to doing. I'm looking forward to being more consistent as a football player and getting better. Working with some of the veteran guys in the NFL, and I'm excited."