Apply suggestions from code review

Co-authored-by: NJason Malinowski <jason@jason-m.com>

src/Compilers/CSharp/Portable/Syntax/CSharpSyntaxTree.cs

@@ -725,7 +725,7 @@ internal bool IsGeneratedCode(SyntaxTreeOptionsProvider? provider, CancellationT
             return provider?.IsGenerated(this, cancellationToken) switch
             {
                 null or GeneratedKind.Unknown => isGeneratedHeuristic(),
-                GeneratedKind kind => kind == GeneratedKind.MarkedGenerated
+                GeneratedKind kind => kind != GeneratedKind.NotGenerated
             };
 
             bool isGeneratedHeuristic()

src/Compilers/Core/Portable/Compilation/GeneratedKind.cs

@@ -7,7 +7,7 @@ namespace Microsoft.CodeAnalysis
     public enum GeneratedKind
     {
         /// <summary>
-        /// Whether the <see cref="SyntaxTree"/> is automatically generated is unknown.
+        /// It is unknown if the <see cref="SyntaxTree"/> is automatically generated.
         /// </summary>
         Unknown,
         /// <summary>