If you want to know how to see this for your self, do the following steps:
1. Open up scratchblocks
2. Type in anything, just make sure it's text.
3. Download the .svg, not .png
4. Upload it on scratch.
5. Click on the text.
6. Click the text tool.
And then boom! There it is.
My theory is, the M.I.T team put in custom fonts for people to use in there graphics, but they had to include other fonts so could make things like blocks, comments, etc. And for scratchblocks to work, they had to use those fonts.
Maybe theres more secret fonts that never got used in Scratch 3.0, I don't know. Maybe you guys could figure it out.