Moyes, back at the London Stadium to replace Manuel Pellegrini following West Ham's alarming slump, had just two days to work with the squad before the match with fellow strugglers Bournemouth.
The Scot clearly had an immediate impact as the Hammers ran out comprehensive 4-0 winners.
"It was a good day - it doesn't get much better. I'm buzzing for everyone," right-back Fredericks told West Ham TV.
"Obviously the gaffer's not been here very long at all. He hasn't had much time with us on the training field but what he has said to us has stuck in our minds. Everything's been short and direct.
"We haven't been out on the training field for hours and hours and hours. With the experience he's got, when he says something, it sticks - we've taken it on board and put it into practice. That's happened so we're buzzing."
With a veiled dig at Pellegrini, Fredericks added: "The boss said it's not about going out and dominating every second of the game. That's not what football's about.
"I think unless you're the top two teams in the world, you need to be solid, not concede goals, and then when you get your chances you need to take them, and fair play to the boys up front, they were clinical, really clinical.
"It was a pretty high-pressure situation that we were in, but I didn't see an ounce of pressure or stress. Even before the game, we switched a few things up, and it really worked.
"I think everyone on the pitch, even the players that came on, looked free and looked like they enjoyed the game."