He’s realised his position that Cass doesn’t follow the evidence is becoming untenable. So he’s now repositioning to say that Cass doesn’t say what we think it says. She was pretty clear I think that the evidence for puberty blockers is shaky and kids should be treated holistically instead.
It was very enjoyable to see the gender activists split into two camps when the report came out - the ones who immediately decided Cass was terrible, the report was transphobic, it was literally genociding millions of trans kids etc, and those (Stonewall, Freddy McConnell et al) who pretended that Cass was simply saying what they'd thought all along, and wasn't it sad that the transphobes hadn't made it possible to have a reasonable debate.
Although Billy is quite dim and very slow to catch on, he has perhaps realised that camp A were on a hiding to nothing, and it was better to align yourself with Camp B if you didn't want to make yourself look utterly ridiculous. Of course, like a kid who imagines that when they close their eyes you can't see them, he seems to imagine no one will notice he's performed a 180 degree about-turn of his original position.