If he had explicitly called for violence directed an particular group or individual you would probably have a point, but then they would have kept him in custody. Rather it seems that he was pulled in for questioning for the same reason as the leftist Shapiro. Someone decided to punish him because they didn't like the tone of his speech. That is what is unacceptable.
Saudi Arabia beheads four, marking 100th execution this year (DPA)
from the article: Police release rabbi arrested for inciting to kill non-Jews