I guess if the rest of the CV was a really strong match, I'd give them a chance but they'd have to do a "technical interview" same as any other junior. I can only speak for myself that I haven't seen many CV's in my environment where 98% of the stack is built on FOSS and 100% of the tooling uses FOSS that an expert in that field has never contributed anything to a FOSS project, has never asked a question on an issue or created an issue (and also lacks any other public facing work like personal projects, talks, blogs, etc). I'd also interview them if they were recommended by a colleague.