Glasgow's reward for the 17-10 win at Thomond Park is a trip to Pretoria to take on Vodacom Bulls.
"We stuck to what we wanted to do, we stuck to our game plan which has done us well all year," Cummings told BBC Radio Scotland.
"We just did it better than what we were doing at the end of the season.
"Munster play a good brand of rugby so it was tough for us. Everyone thinks of Munster as a physical up front team, but they move the ball a lot."
Sebastian Cancelliere went over for Glasgow's second try after Tom Jordan ran back a Munster kick from deep in his own half with Cummings admitting he "didn't even know what happened."
"I was setting up for something completely different than I was supposed to do. Just turned round and there was a line break. Some unbelievable tries, I think even Steyno's [Kyle Steyn] just comes off the back of our defence.
"We put in some effort for that game and we needed it to get the win.
"It was tough, it was physical. We all work hard for each other, we feel like we're a hardworking team that's very close and we have to train hard as well. We put the effort in but we feel that we need to to get the results from it."