Yes. You let him do exactly what he said he was going to do - which is (in theory) quietly cross the road. That is not illegal and is a reasonable request. The second he started attempting to disrupt the march and deviating from what he said he was going to do you arrest him under Section 5 of the Public Acts Order

(a) uses threatening [or abusive] words or behaviour, or disorderly behaviour, or. (b) displays any writing, sign or other visible representation which is threatening [or abusive], within the hearing or sight of a person likely to be caused harassment, alarm or distress thereby."

Then you prove everything that was said. What you don't do is prevent him from crossing the road because he is 'openly jewish' - because, and this is important, those optics make you sound like you support anti-semitism.

BUT.... and this is important.

You also have to arrest anyone else who attempts to engage with him with abusive words or threatening behaviour. I suspect that is why this didn't happen.... and why I've questioned the supposition that prima facie it was a peaceful march. I think, as with many complicated issues, there are fuckwits either side of the fence.