I agree. The only thing they are saying is that you will not be considered well if you ever want to go back there. They would get themselves into trouble if they shared performance with third parties. To be honest, something made you want to leave. Whatever that thing is will still be there in the future. So it sounds like returning would be out. Still, people move in and out of positions and in all likelyhood any future application you might have with them culd be considered. They woudl want to know more details about the statement. If you say what you said in your post I'd say you might be OK.
In the software world, some examples of inappropriate usage are: EJB for a small ecommerce app; extreme programming for a short-term project with stable requirements; Struts for a web project where plain old JSP + JavaBeans would do the job handsomely; taglibs where adding a new meta-language rewards the team with nothing but confusion; or Model 2, design pattern mania where someone on the team has read GOF and hence decided to shoehorn as many design patterns as possible into their design.
If a camel is a horse designed by a committee, then a consensus forecast is a camel's behind. -- Edgar R. Fiedler