The authors published a clarification, in it they recommand:

There are now numerous reports of health workers wearing home made cloth masks, or re-using disposable mask and respirators, and asking for guidance. If health workers choose to work in these circumstances, guidance should be given around the use.

There have been a number of laboratory studies looking at the effectiveness of different types of cloth materials, single versus multiple layers and about the role that filters can play. However, none have been tested in a clinical trial for efficacy. If health workers choose to work using cloth masks, we suggest that they have at least two and cycle them, so that each one can be washed and dried after daily use. Sanitizer spray or UV disinfection boxes can be used to clean them during breaks in a single day. These are pragmatic, rather than evidence-based suggestions, given the situation.

Unfortunately that study doesn't cover the question we want answered:

The control arm was ‘standard practice’, which comprised mask use in a high proportion of par- ticipants. As such (without a no-mask control), the finding of a much higher rate of infection in the cloth mask arm could be interpreted as harm caused by cloth masks, efficacy of medical masks, or most likely a combination of both

So the study found evidence that surgical masks are better than cloth masks, but doesn't say anything about whether cloth mask are better than nothing.

The study authors speculate that cloth masks are detrimental, but after reading through the study again, I'm pretty sure they provide absolutely no evidence for that (2 out of 1607 people in their study didn't wear masks).