Sephardic Jews DNA results

[Riverman]

I don't trust such estimates too much. The most trustworthy results come from matches which share solid segments with a person. Like if you have a couple of Sephardic matches on a specific area of a chromosome, that would be better evidence than ethnicity estimates of some sort, which might be skewed by bad fitting references or very old admixture events.
If we are talking about 1500 and later, there is a chance, if the admixture is real, that you still have some matches in that direction. To check that seems to be the better way to go, IMHO.

As said two matches on my heritage Riverman with two Israeli.

Take in account that the Y-DNA is exclusive Levantine and E-V22 is core semitic.

In we must take in account that this Y-DNA suvived the reconsquista, went 'undercover' in Frisians catholics and when some were part of the Sepharadim the Holocaust did probably the rest.

We are talking about (end) 17th century, 7 generations ago, and the Jews shared at that time a worship house in Leeuwarden next to my ancestors lived (and participated).

Two is not a lot, though. But given that the ancestor might have lived in the 16th century, its possible he left no autosomal heritage in your family at all. Or you might have autosomal Sephardic ancestry, but not from your direct paternal ancestor. Many alternative options, I'd say.
Without a more recent paternal lineage match, it remains speculative.