The Plasmodium parasite doesn't seem to have any special characteristics (ie size, spectral response) that would make it detectable by such a device. You can skip the sample size issue by assuming the diagnostic will run for hours or days, but I don't see any theoretical foundation this device could be based on.
Also the obsession of the website with the smartphone interface is kind of sketchy and makes it look (more) like a scam to me.
Edit: I looked further into it, the price is given by the royal academy of engineering. Taken from their website [1]:
" Gitta wins the first prize of UK £25,000 (124 million Ugandan shillings). At an awards ceremony in Nairobi, Kenya on 13 June 2018, four finalists from across sub-Saharan Africa delivered presentations, before Africa Prize judges and a live audience voted for the most promising engineering innovation."
Which means that a live audience of non-technical people were involved in the choice, and, to my opinion, from the rest of the content, this is a feel-good kind of competition with soft goals like promoting innovation and training young people, not the kind of competition that awards working ideas.
[1] https://www.raeng.org.uk/news/news-releases/2018/june/uganda...