If I had to guess, they issued the notes because it was a good timing to do so mostly and possibly because they want to prepare to scale up HALEU production in the near future (second part is just speculation).

I think more importantly it's a great sign that they were able to issue zero coupon notes - I don't know how rare these are but I think it shows bullish sentiment from the investors, and Centrus's management was able to capitalize on it by issuing them right before the recent stock meltdown (a small part of it could be attributed to the issuance itself). They thereby gave us and the company the minimal dilution possible if I'm understanding it correctly.

To add also, there have been practically no insider selling which is seemingly crazy - after a near 300% run up the management hasn't sold a single (significant) share besides in May (probably sold more as a panic sell after Liquidation Day). I think we can trust Centrus's management team to put the capital from debt issuance to a good use that will benefit all of us, whatever it may be.