I wondered about this sentence.
If you would apply scripting functionality to serve long-running websocket or HTTP/2 connections I'm sure garbage collection would be necessary. However if the scripts are really per request and not per connection then it could work - but the capabilites would be much more limited then what you can do in other scripted-webserver-environments (e.g. node).
A VM context could be cheap to create and include an amount of memory above what that script uses for its lifetime. Meaning a single allocation and then the whole thing gets free'd at the end of execution. Analogous to how CGIs execute.