Libcurl receives encrypted data from 538

I am using libcurl to get some data online. Specifically, I want to keep updated on the information here

https://projects.fivethirtyeight.com/pollster-ratings/?ex_cid=irpromo

for research purposes. However, when I use libcurl to pull that data, the result looks encrypted:

‹ ì½ÛVãȺïy¿ŸÂ5Ö{‰l…ÎÊšUk@f’ df‘7:„m-¹t ÌÞ=F¿F?

It works okay with other https sites so can you tell me why is it not working here?

Thanks for any help.