Publishing source code is protected under the First Amendment. Therefore the US government cannot stop anyone from publishing open source software, and once it is available from a web site it is impossible to stop anyone else getting it.
However any kind of support contract (such as this) or other commercial arrangement would fall under the definition of "trade" and be banned.
Update in response to comments about ITAR.
The USA International Traffic in Arms Regulations still cover cryptographic software. However any attempt to prosecute an open source project for publishing cryptographic software would run up against the First Amendment. In 2008 the 9th Circuit found that open source cryptographic software is covered under the First Amendment, and hence the use of ITAR to restrict its publication is unconstitutional.
The US government declined to push this case to the Supreme Court, and no other similar cases have arisen since. In the meantime strong open source cryptographic software has been made widely available from within the USA without US government permission (Linus Torvalds is resident in the US).
In theory the US government might launch a case against an open source project, win the appeal in another circuit, and hence create a circuit split which the Supreme Court would have to resolve. However they have now had over 10 years to try this, and the longer they wait the less likely such a case is to succeed.