yes, could be a lot of things but this is definitely a factor. In some countries testing has been so low that the only people who get tested are those who come to hospital or show symptoms.
I have seen one suggestion made that we do a regime of testing like we do with political polls i.e. a large enough stratified sample across the community is tested in their homes, at work etc and the results used to extrapolate the real level of infection rate and perhaps also give an idea of targeting of testing.
Has some merit imo
There are some countries way behind on testing. I was reading over the weekend that the UK have only just opened up testing for all medical personnel that haven't been overseas or in contact with someone from overseas. At the same time Australia is planning on testing anyone that has any symptoms. Would explain why our rate of testing per million people is about double the UK. It sounds like testing in Australia will most likely double over the next 2 weeks from where we are currently so somewhere around 1m tests.