Republic of Ireland forward spoke to The Football Show about the motivational England video and how it made into the public sphere.
"[I was] surprised," Horgan said.
"He was very good, he was great around the place and I don't know the ins and outs of it but he was a very good coach."
As for the video itself, Horgan expressed his surprise that it made it into the media.
"I don't remember most of it. I remember that there was Ray Houghton's header, there was bits and pieces - nothing major.
"I don't even really remember it - nothing stuck out to me as 'Jesus, this is a bit much' - I didn't think there was anything in it.
"I was very surprised when it came out, that there was a problem. I hadn't really heard anything about it."
As to how the leak occurred, Horgan believes that this is the environment of modern football.
"It is very easy for anything to get into the papers. I don't know how or why it got in there. That is the nature of football as it is now.
"There are lots of different agendas and lots of different things going on. It was a strange time but I was glad that it was parked so quickly."
Horgan says that he has 'no idea' about who leaked the information about the video to the UK press.
"I wouldn't have thought that there was anyone in the setup that did not have the best interests of the team at heart. Everyone wants to go out and win, playing well. From what I saw, people were enjoying it.
"People were enjoying the camps even though they were crazy with ins and outs. I couldn't say it was him, him or him. I just don't know."
Horgan believes that the video situation is similar to the end of a prior managerial regime.
"In a way, football never ceases to amaze with the kind of stuff that goes on. Storm in a teacup-type things; press for press' sake.
"It was a nice easy one for people who wanted to put the boot into [Stephen] Kenny because results hadn't been great, and they probably felt that this was another little kick.
"Towards the end of the Martin O'Neill era, there was a lot of stuff that was held until the opportune moment and then unleashed on him."