The instrumentation key / connection string is how applications authenticate and send telemetry to the App Insights resource. It's the credential the SDK or auto-instrumentation agent uses to say "this data belongs to this App Insights component." It has always existed and still exists on workspace-based resources.
The Log Analytics workspace ID is where that telemetry gets stored once it arrives. When Microsoft moved App Insights to workspace-based mode, they changed the backend storage from a proprietary per-resource store to a Log Analytics workspace, which gives you the App* tables and cross-resource querying via _ResourceId. But the front-door ingestion mechanism — the instrumentation key — stayed the same.
So the flow is:

Application (SDK / auto-instrumentation)
    │
    │  authenticates with instrumentation key
    ▼
App Insights ingestion endpoint
    │
    │  stores data in
    ▼
Log Analytics Workspace (AppRequests, AppTraces, AppExceptions...)
    │
    │  surfaced back through
    ▼
App Insights query endpoint (requests, traces, exceptions...)

The key is the front door. The workspace is the filing cabinet behind it. You need both to exist and be correctly linked for the resource to work — finding both on the same resource is exactly what you'd expect.
What would be unusual is finding a workspace-based resource with no instrumentation key, or a classic resource (pre-workspace) with a workspace ID. The combination you found is the standard modern setup.