What is the link between address and use of the UTXO?
Because the address you are using is a P2SH-P2WPKH address as you mention (sh (wpkh ())), you get the output

&quot;isscript&quot;: true,
&quot;iswitness&quot;: false

It is talking only about the top level (P2SH), because it is a P2SH address, regardless of what the script &quot;inside&quot; it encodes. It doesn't &quot;see&quot; the underlying P2WPKH when you call validateaddress. The only time isscript and iswitness are both true, is for P2WSH addresses. You can view the code which creates this RPC isscript/iswitness output here.
When you spend it, you reveal the script inside the P2SH. Because it is a P2WPKH script, which is OP_0 &lt;keyhash&gt;, that script is then evaluated as such (using the key/signature data in the witness).