Some studies, as above, show it is as bad or worse so context may be important.
However, from the conclusion of the study you posted
"These results suggest that dietary protein and soy isoflavones, in the context of comprehensive lifestyle 25 changes, may not significantly alter IGF-1. However, given the recent literature indicating that high intake of protein rich in essential amino acids (animal or soy protein) may increase IGF-1, it may be prudent for men with early stage prostate cancer not to exceed dietary protein recommendations."
The original trials by this group included soy protein but after they saw IGF-1 levels were still high, then removed the soy protein from subsequent trials.
The CR research also limits all protein, though, I do agree that in some aspects animal protein (ie, methionine), may be worse