Yes, it’s a temperature differential “hot air” engine. The use of cold pumped water through the cooling jacket enhances efficiency. I have read that the cycle of this engine is not technically Stirling, allegedly it is better efficiency, but I don’t understand the distinction. I do like it though, looks like a design that could be readily adapted to tubular steel frame, and some components, and welded design.
It was mass produced, but couldn’t match the immediate start up or compact power of gasoline engines.