The leaked Podesta content goes back quite some time, so yes, there are old emails in there that still had DKIM signatures from a 1024 key.
The email in question is not one of those, and uses the 2048 bit key (emailid/2038).
Also, your assertion that hillaryclinton.com was compromised ... where did you get that? Those emails were released by the govt because of FOIA requests. The DNC was hacked and therefore "compromised" by persons unknown (but some people did a lousy job of attributing it to Russia). The DNC is not hillaryclinton.com, tho.
Yeah, you're correct a lot of the emails use 2048-bit RSA for the DKIM signature. I trust those more than the 1024-bit signatures. I have a pretty heavy distrust of all of this, because from the sidelines I can't tell who is manipulating what. I don't blindly trust the cryptography because I don't know the capabilities of the adversary or what side channel attacks were present. That probably sounds stupid, but I'm feeling a whole lot of distrust of everyone involved.
Following that, my assertion that hillaryclinton.com was compromised was completely evidence-free. That's a personal assumption due to the significant lack of security expertise by the maintainer of the server. There are plenty of emails sent between clintonemail.com and the DNC gmail accounts that CC Podesta and were included in the Wikileaks dumps.
The DNC was hacked by two Russian actors according to CrowdStrike. I trust CrowdStrike in this assessment.
Others are signed by hillaryclinton.com, which was likely compromised as well.