I'm not a lawyer either but I don't see what's wrong with that argument. The tool that Beeper built isn't infringing any laws, reverse engineering in this context is perfectly legal. They're not responsible for their users' use of the tools they build and their consequent violation of the TOS.
That's not generally true in practice. Especially when it is marketed to end users as a TOS-violating product and doubly so when it was originally a commercialized product.