What's interesting from the photo is that there's a second fence between where the trees were and the railway line
I don't know why there's a second fence but it seems everything between the track and the second fence is untouched.
There is no second fence. The photo you provided links to a picture taken from the top of the cutting on the other side from the houses. If you look at the video or photos on the Bristol Evening Post website (no idea why they have put it as a video when more still photographs would have sufficed) you can see that the trees cut down were immediately over the fence on the cutting, right next to the railway line.
See attached Screenshot from the video which shows the situation. This bit of the video was taken from the platform at Montpelier station. Also see https://i2-prod.bristolpost.co.uk/i...e/ALTERNATES/s615b/BRJB20180126A-005-1JPG.jpg for a photo taken from the same location.