While I don't think it's necessarily sufficient to justify defederating their whole instance, it's worth noting that the reason they gave is definitely accurate. The BBC is incredibly transphobic. Here's a Wikipedia article about one of their worst, most prominent instances. It's no more so than is pretty standard in Britain these days, sadly, but that's not a good bar to measure yourself against.

There was a big campaign of utilising the BBC's complaints process to complain about the many flaws in that article. Here's a YouTube video by one person involved in that campaign. That's part 1 of 4 as the different stages of the process played out. The TL;DW is that the BBC ended up ignoring the complaints and ended up picking up on small flaws in the way the complaint was phrased (or just making up flaws where they didn't really exist) to use as an excuse to "respond" saying there was no problem with their journalistic standards.