I think the report refers to teachers who are training to be primary school teachers.
If I'm nor mistaken, every primary school teacher teaches all the subjects. Because of the relatively low quality of the Education degree intake, many of them are themselves weak in maths to begin with. In my mind, all attempts to try to train them to teach maths would be mostly futile. Long ago, when jobs opportunities were more limited, the quality of education trainees, mainly at the Teachers Training Colleges of each state, were much higher.
A very simple solution, it would seem to me, is for each school to have a number of Maths and Science teaching specialist teachers, in the more senior years of primary school, to be given the task of teaching these subjects. We often have teachers who are very good at teaching History and English, but hopeless at Maths - such teachers are valuable but should not be made to teach Yr 5 or Yr 6 Maths.
Alternatively, if the authorities are serious about the situation, they should mandate, as a requirement for all seeking to be trained as primary school teachers that they have a minimum ATAR of 85 and a minimum of a Band 5 for HSC Maths(2U); those doing General Maths should be automatically precluded since they have shown themselves to be wimps in maths.
As for shortage of qualified Maths teachers, I know of the case of a teacher, fully qualified to teach High School Maths who was unable to get a job for over a year. He went to a top selective school and graduated from Sydney U. He could not even get an interview when he applied for positions in country NSW! So I find all these talks of shortage of qualified High School Maths teachers difficult to comprehend; perhaps it is just a myth.