From the abstract:

"Studies suggest muscle loss with these medications (as indicated by decreases in fat-free mass [FFM]) ranges from 25% to 39% of the total weight lost over 36–72 weeks. This substantial muscle loss can be largely attributed to the magnitude of weight loss, rather than by an independent effect of GLP-1 receptor agonists, although this hypothesis must be tested. By comparison, non-pharmacological caloric restriction studies with smaller magnitudes of weight loss result in 10–30% FFM losses."

The "surprising" part is kinda bullshit, and implies there's something special about glp-1s. It is the opposite of surprising that weight loss includes a lean mass loss.

That said, being skinnyfat is probably bad for you and the idea that you should work to preserve/build muscle and not only lose weight is a good one.