Publishing single applications is a relatively popular use case for ThinLinc. Sadly, it is poorly documented in the ThinLinc Administrator's Guide. Currently, it is only briefly mentioned in the man page of tl-single-app and in the "Start a program" section in the client configuration chapter (https://www.cendio.com/resources/docs/tag/client_options_advanced.html). It is, for example, not mentioned in the part about profile configuration, which is the typical way of configuring single application publishing.
A very short paragraph about this was added in commit r42003 for bug 5499.