The 23-year-old goalkeeper joined Aston Villa on loan until the end of the season after being frozen out at Manchester United, behind the likes of David De Gea and Sergio Romero.
With first team opportunities limited, Johnstone opted to join the Championship club on loan, but says he could have moved to a Premier League side.
He said: "I did have other clubs interested in taking me, including a couple in the Premier League, but this was where I wanted to come.
"Steve Bruce didn't have to say very much to me, to be honest. The chance to come and work with him and at a club like Aston Villa seemed too good to turn down.
"The club is massive and it is exciting to be here. Seeing a stadium like Villa Park close to being full every week and with the following that the club gets away from home is all you need to know".
Johnstone also showed his appreciation for Manchester United manager Jose Mourinho, who let him leave the club to play first team football.
He said: "I signed a new contract recently but I told the manager that I wanted to get out to play games, and to be fair to him he understood that and I'm grateful for his help.
'Working with David de Gea and the other goalkeepers at Old Trafford has been great experience, as well as learning from the staff that Jose Mourinho has assembled.
"But I'm not someone who just wants to sit around. I told him at the start of the season that I wanted to get more experience. I respected his decision then that he wanted me to stay, and now I'm just delighted at the chance to hopefully play some games.
"I've not been made any promises. It is up to me to work hard and try to show that I should be in Aston Villa's team, and that is what I will try to do".