Hi @市川_智一
The data-asana-gid portion of the returned tag is their User gid.
See Rich Text, especially this part:
Suppose a user with a name of "Tim" and a user GID of "53421" is @-mentioned. This will create a link to their "My Tasks" which is a project with a GID of "56789"
* The raw link generated in Asana will be https://app.asana.com/0/56789/list.
* The <a> tag returned in the API will be <a href="https://app.asana.com/0/56789/list" data-asana-accessible="true" data-asana-dynamic="true" data-asana-type="user" data-asana-gid="54321">@Tim</a>.