The Dane and his Mercedes rival came together at Turn 4 on the opening lap at Barcelona last weekend as he tried an overtaking move around the outside.
On the team radio immediately afterwards, Magnussen reckoned that Hamilton had deliberately opened up his steering, although he later clarified that those remarks were simply made in the heat of the moment.
But having watched the incident again in the days after the Spanish race, Magnussen said that he now believed Hamilton was completely innocent.
Instead, he thinks it was just unfortunate circumstances, as he said with hindsight he wishes he had left the seven-time world champion a bit more space.
Speaking about the clash ahead of the Monaco Grand Prix, Magnussen said: "I had a chance to look at it and of course I changed my view on that.
"I had the feeling when I was on the track that he opened the steering. But that's not what happened. He just got in the slipstream of the Ferrari, and understeered a tiny bit.
"I was super close to him. I didn't give him much room for error, I gave no margin. So we touched. It was unfortunate."
Magnussen said that there were no regrets about attempting to pull off a lap one pass like that, but just regrets his trajectory not being slightly different.
"I just wish I had turned in one millisecond later," said the Haas driver. "But also in a corner like that, if you're going to go around the outside, you want to be as close to him as possible. You don't want to go too wide and go on to the dirty part of the track. That's what I did.
"We touched unfortunately. There was also a lot of bad luck in that. If I had just been a little bit further forward when we hit, we would have hit rim to rim and it would have been different.
"But unfortunately I just hit with his side at the tyre and it was a puncture. It was bad luck. I wish I had given him slightly more room."
The incident put Hamilton and Magnussen to the back of the pack on the opening lap.
While Hamilton was able to stage a strong recovery and finish fifth, despite engine problems late on, Magnussen could not make similar progress and came home 17th.