Google "lobster bisque" and of the first couple of pages of recipe hits, the vast majority are thickened with roux.
Most "classic" French sources make bisques with a fish veloute, which has as you know, a roux base. I refer espicially to Pellaprat and E. Sainte Ange. I'm not sure whether Escoffier broke away from the dominant line, or whether Pellaprat and Sainte Ange represented the next generation. At any rate, Escoffier's method which became the method for Ritz hotels worldwide up into the fifties, involved pounding the shells with raw rice in a giant mortar and pestle -- until all was powdered. You could certainly do that today with the right blender or processor.
I'm pretty sure Julia Child's lobster bisque used flour -- but can't find her recipe. Maybe someone else can.
Modern French recipes (also researched on google "bisque de homard") are split between structuring without a starch thickener, ground rice and/or a flour based roux or beurre manie, in an amount besoin. I only looked at the first dozen or so hits, but the impression I got was that flour in the form of roux or beurre manie was the preferred thickener.
The bulk of American sources seem to call for flour. My first edition of Joy of Cooking calls for flour, as do the later editions. My old two volume Gourmet Cookbook calls for flour, and does Craig Claiborne's generation of the NY Times cookbook. On the other hand, modern American "gourmet" recipes from sources such as Gourmet, Bon Apetit, and Saveur call for cornstarch.
In a restaurant setting, where long holding was required, I'd choose flour over cornstarch.
Chef Ray's "powdered lobster shell" is almost certainly used for color (especially where there's no tomato paste) and flavor, not for thickening. It doesn't thicken.
Bottom line: Abe, you probably tasted exactly what you thought you tasted. Going a bit deeper: There's no reason why you couldn't make an exceptional bisque with a flour based roux, and there are several perfectly good alternatives.