In addition to the code snippet you have shared, you will also need to attach the OnAjaxUpdate event to the Grid and update the ContentTemplateContainer with the ToolTip value.
Sample C# code
protected void OnAjaxUpdate(object sender, ToolTipUpdateEventArgs args)
string ttValue = args.Value;
I have updated the documentation article to explicitly mention that. Here is the Git commit: docs(tooltip): fix snippets. Changes will be applied within an hour counting from the time the Commit was pushed to the production branch.
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