Assistant General Manager Jeremy O'Day said that the trade happened quickly last night and was not part of long-term negotiations between the two teams.
"You're in constant contact with guys throughout the season," O'Day said Saturday afternoon. "Names do get thrown back and forth and those were the two names that both teams were interested in."
According to O'Day, the trade was made in an effort to make the Roughriders better. Linebacker, he said, was one of the positions the Riders specifically wanted to improve on.
"We were able to get one of the premier Canadian linebackers in the league with Shea," he told reporters.
Last season, Emry led the Argos with 72 defensive tackles, and also notched one forced fumble and a sack. He started all 18 regular season games.
"[Emrys] really excited to come here. We had a conversation with him this morning, he said as soon as he heard he went and put his green lumberjack shirt on, so he's excited. He's excited to get here," O'Day said.
Foley, on the other hand, was disappointed to hear the news that he was leaving Rider Nation.
"When we talked to him this morning he was bummed out," O'Day said. "He was in a place where he really wanted to be, he liked the fans here, liked the team. He was very open with that for the whole time he was here."
Foley, 32, had just re-signed with Saskatchewan in December. He was the team's top Canadian in 2014 with a career-high 12 quarterback sacks.
Emry is entering his eighth year in the CFL. He spent six of them with the Montreal Alouettes before signing with the Argonauts last season.
He is also a two-time Grey Cup champion, winning with the Alouettes in 2009 and 2010.