Many products from China have poor documentation, and I think the product description of 20A / 20mA is just for illustrating the current ratio between primary and secondary windings, instead of the maximum supported current . I can find another image from the China online store mentioning that it can support up to 60A / 60mA. The Chinese words “以下规格都可使用” in the image means “The following specification can be used”.
Frankly, with the primary current of 50 amps, it only induces 50mA in the secondary windings. 50mA is just a little current and should not be problem. I am using it for all my 32A circuit breakers, and another post in the forum (Solid core CTs no more? - #2 by fermulator) also mentioned that it should be capable to support 50A. I have already using more than twenty DL-CT08CL2 for myself, and this product is in good quality given its low price.
Nevertheless, I am just a hobbyist and you may wish to obtain second opinion from your electrician.