Yes, the rampant spread of covid will make it difficult to make the case it was caught at work, unless the work is somewhere covid is known to be like healthcare or where an outbreak is known. Unless and until we have sufficient infection control measures in most places it will continue to be difficult to know where one was exposed.
Unfortunately it’s already the norm in many workplaces to not inform employees of outbreaks. There’s little to no requirements for reporting cases so businesses have no responsibility to keep covid out of the workplace and people are getting sick at work. This ruling is a result of that reality, not a precipitator.