A concerning thing is that a dev database username and password was committed to multiple files, like this: https://github.com/propublica/nyc-dna-software/blob/master/F....
The actual codebase itself may be pretty old so WebForms isn't a surprise - the SLN file indicates it was saved with Visual Studio 2010 (https://github.com/propublica/nyc-dna-software/blob/338a1b86...).
Webforms is likely a client request as well, but also keep in mind that as shitty as webforms is it let's you throw functionality together faster than almost anything else. Again proly contractors
The funny comments others mentioned is another clue that this was not developed internally. I miss that about being a consulting company... The client is usually hiring you because they have no idea what they're doing so rest assured nobody there will ever look at the code.